Methods and devices to decrease tissue trauma during surgery

ABSTRACT

Methods and devices are disclosed to reduce tissue trauma when a physician retracts a patient&#39;s tissues for surgery. In one part, methods and devices are disclosed for controlling retraction force and pace. In another part, methods and devices are disclosed for oscillating force when opening. In another part, methods and devices are disclosed for detecting trauma during retraction. In another part, methods and devices are disclosed for balancing forces on multiple retraction elements. In another part, methods and devices are disclosed for reducing forces in multiple dimensions. In another part, methods and devices are disclosed for engaging ribs. In another part, methods and devices are disclosed to compensate for deformation of a retractor under load. In another part, methods and devices are disclosed that combine these methods and devices. In another part, methods and devices are disclosed for controlling pressure inside inflatable devices used for deforming biological tissues.

PRIORITY AND RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 61/395,915, entitled “METHODS AND DEVICES TO DECREASETISSUE TRAUMA DURING SURGERY,” filed on May 19, 2010, which isincorporated herein in its entirety.

The present application is a continuation-in-part Application of U.S.patent application Ser. No. 12/422,584, entitled “METHODS AND DEVICES TODECREASE TISSUE TRAUMA DURING SURGERY,” filed on Apr. 13, 2009, which isincorporated herein by reference in its entirety, which claims priorityto:

-   -   a. U.S. patent application Ser. No. 12/422,584 claims priority        to U.S. Provisional Patent Application No. 61/123,806, entitled        “OSCILLATING LOADING TO MINIMIZE TISSUE TRAUMA DURING SURGICAL        PROCEDURES,” filed on Apr. 11, 2008, which is incorporated        herein by reference in its entirety, and    -   b. U.S. patent application Ser. No. 12/422,584 claims priority        to U.S. Provisional Patent Application No. 61/044,154, entitled        “METHODS FOR DETECTING TISSUE TRAUMA DURING SURGICAL        RETRACTION,” filed on Apr. 11, 2008, which is incorporated        herein by reference in its entirety, and    -   c. U.S. patent application Ser. No. 12/422,584 claims priority        to U.S. Provisional Patent Application No. 61/127,575, entitled        “SURGICAL RETRACTOR ARMS FOR REDUCED TISSUE TRAUMA,” filed on        May 14, 2008, which is incorporated herein by reference in its        entirety, and    -   d. U.S. patent application Ser. No. 12/422,584 claims priority        to U.S. Provisional Patent Application No. 61/127,491, entitled        “APPARATUS AND METHODS FOR REDUCING MECHANICAL LOADING AND        TISSUE DAMAGE DURING MEDICAL PROCEDURES,” filed on May 14, 2008,        which is incorporated herein by reference in its entirety, and    -   e. U.S. patent application Ser. No. 12/422,584 claims priority        to U.S. Provisional Patent Application No. 61/131,752, entitled        “APPARATUS AND METHODS FOR ENGAGING HARD TISSUES TO AVOID SOFT        TISSUE DAMAGE DURING MEDICAL PROCEDURES,” filed on Jun. 12,        2008, which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The field of the disclosure relates to spreaders, retractors,angioplasty balloons, and retraction devices used to deform tissueduring surgery or other medical procedures.

BACKGROUND

Deformation of tissues is commonly performed during surgery or othermedical procedures either to achieve surgical access or to specificallyalter the dimensions of one part of the anatomy. Examples ofdeformations of tissue for surgical access include spreading ribs duringa thoracotomy, spreading a bisected sternum during a sternotomy, andseparating the vertebrae of the spine for surgery on the intervertebraldisk. Examples of deformation of tissues to alter the dimensions of thetissue include angioplasty to open blocked arteries, valvuloplasty toenlarge heart valves, and distraction to adjust the position ofvertebrae. Such deformations are collectively referred to herein as“retraction”.

Spreaders, retractors, distractors, and even angioplasty balloons(collectively called “retractors” here) can impose significant forces onthe surrounding tissues during retraction. The resulting strain on thesetissues, and on associated tissues such as the ligaments attaching ribsto vertebrae, can be large, leading to damage of these tissues,including the fracture of ribs and the rupture or irreversibledeformation of ligaments and other fibrous tissues.

Retraction occurs in two different phases—deforming the tissue (referredto herein as the first phase or retraction) and holding the tissue atthat deformation (referred to herein as the second phase of retraction).Usually both are done with the same instrument. For example, a ribspreader is used both to force the ribs apart during a thoracotomy andto hold the ribs apart during the surgical procedure. Sometimes twodifferent instruments are used, especially if the deformation is to bepermanent. For example, an angioplasty balloon is used to force open anatherosclerotic plaque, and then a stent is used to hold the arteryopen; or a distractor is used to separate vertebrae, and a metal plateis used to secure the vertebrae in that position. An example of twodifferent instruments being used when the deformation is not permanentis disclosed in U.S. Pat. No. 5,201,325 by McEwen (McEwen, Auchinleck etal. 1993), therein a surgeon manually retract an incision with adisclosed retractor blade, and an automated mechanism is then used tohold the incision open. In the medical literature, both phases arefrequently referred to as retraction.

Both phases of retraction traumatize tissue. Trauma from the first phaseof retraction can include the rending and tearing of tissues—bones bendand break; muscles stretch beyond normal limits; ligaments and otherconnective tissues stretch and tear; or nerves are stretched. Traumafrom the second phase of retraction can include ischemia of the tissuedue to elevated tissue pressure, for example, under a retractor blade;blockage of nerves; and blockage of blood vessels causing ischemia intissues distant from retraction.

Tissue trauma and ensuing complications resulting from retraction can begreater than the trauma resulting from the medical procedure thatrequired the retraction. For example, thoracotomies are extremelytraumatic, and can result in post-surgical pain and respiratorycomplications that exceed that of the thoracic procedure, such as a lungsegmentectomy.

There is, therefore, need for improved methods and devices to performone or both phases of retraction.

SUMMARY OF THE DETAILED DESCRIPTION

The embodiments disclosed herein provide retraction devices adapted toretract tissue. In one embodiment, such a device comprises at least onepair of opposed retraction members, with each retraction member beingable to operably engage the tissue to be retracted. A drive mechanism isoperably engaged with at least one of the retraction members in each ofthe at least one pair of retraction members. The drive mechanism isadapted to provide a continuous, smooth deformation of the tissue,following, for example, a parabolic distance/time curve duringretraction.

In another embodiment, retraction devices that are adapted to provide aconstant force during retraction of tissue. The retraction devicescomprise at least one retraction member, with the at least oneretraction member being able to operably engage the tissue to beretracted. A drive mechanism is operably engaged with the at least oneretraction member.

In another embodiment, a retraction device includes automated controlwhile detecting imminent fracture. In this manner, the automated controlcomprises measuring the retraction force and monitoring for transientsin the force signal, such as a negative-going spike or an increasedvariance in the force signal.

In another embodiment, a retraction device includes at least one pad incontact with the margins of an incision. The pad is adapted to cool thetissue at and surrounding the margin of the incision to reduceinflammation and minimize temporary ischemia of the tissue.

In another embodiment, a retraction device includes at least one pad incontact with the margins of an incision. The pad is adapted to elutepharmacologically active compounds into the tissues at the margin of theincision to achieve beneficial outcomes, such as hemostasis or reducedinflammation.

In another embodiment, a retraction device is provided to retracttissue. In this manner, multiple tissue engagers that automaticallyself-balance force comprise at least one retraction member, with the atleast one retraction member being able to operably engage the tissue tobe retracted. A drive mechanism is operably engaged with the at leastone retraction member.

In another embodiment, a retraction device is provided to retract tissuewith forces aligned with the retraction. The retraction device comprisesat least one pair of opposed retraction members, with each retractionmember being able to operably engage the tissue to be retracted. A drivemechanism is operably engaged with at least one of the retractionmembers in each of the at least one pair of retraction members. At leastone of the retraction members comprises an arm that can rotate around anaxis perpendicular to the drive axis connecting the two retractionmembers, permitting the retraction members to align with respect to theretraction.

In another embodiment, a retraction device is provided to retracttissue. In this manner, the retraction member comprises a retractor armfitted with tissue engagers that engage hard tissues while minimizingdeformation of soft tissues.

In another embodiment, a retraction device to retract tissues isdisclosed wherein the creep of the tissues is accommodated. Theretraction device comprises at least one pair of opposed retractionmembers, with each retraction member being able to operably engage thetissue to be retracted. A servo-drive mechanism is operably engaged withat least one of the retraction members in each of the at least one pairof retraction members such that the retraction members are driven apart.At least one retraction member comprises a retractor arm fitted with aforce measuring device that measures force on the at least oneretraction member. This measured force is used to determine thedeformation of the retraction member, and the servo-drive mechanismadjusts the separation of the retraction members to accommodate forcreep of the tissues.

In another embodiment a thoracic retractor for performing a thoracotomyis disclosed, comprising a linear drive element having at least twoarms, with at least one of them moveable along the linear drive element,and at least one self-balancing tissue engager associated with each arm.The self-balancing tissue engager comprises a first rotary joint betweenthe arm and a first balance bar, which has additional rotary joints oneach of its two ends to which second balance bars join, and each balancebar has rotary joints on each of its two ends to which join descenderposts that engage a rib on one side of the incision. Opposing arms andassociated tissue engagers thus engage opposing ribs on each side of anincision and retraction in opposing directions along the linear driveelement spreads the ribs apart to retract the thoracic tissue.

In another embodiment, two opposing arms are each associated with adoubletree balance bar, each doubletree balance bar having two ends towhich rotatably join swingletree balance bars, one swingletree balancebar on each end of the doubletree balance bar. Each swingletree balancebar has two ends to which rotatably mount a descender post each of whichengages a rib. There are thus four descender posts, with forcesautomatically balancing through the doubletree and swingletree balancebars, that engage a rib.

In another embodiment, a tissue engager for thoracic retraction isdisclosed, comprising a balancing assembly having at least one descenderpost descending from at least one balance bar. The descender postcomprises an elongate member with a first rib-forcing surface and a hookelement with a second rib-forcing surface such that a gap region isformed between the first and second rib-forcing surfaces, the gap regionbeing concave and extending far enough in the direction of retraction toplace the second rib-forcing surface away from the neurovascular bundle.

In another embodiment, the concave shape of the gap region of thedescender post is further defined as a tapered hollow defined by a taperpoint.

In another embodiment, the taper of the descender post forms an acuteangle.

In another embodiment, the tissue engager has a plurality of descenderposts.

In another embodiment, the tissue engager has a plurality of balanceddescender posts.

In another embodiment, a tissue engager for thoracic retraction isdisclosed, comprising at least one retraction bar capable of movingalong a direction of retraction and having at least one descender postdescending into the incision. The descender post has an elongate member,having two ends with a first rib-forcing surface adjacent to the secondend and the first end joining a balance bar at a rotatable mount, and ahook element adjoining the second end of the second end of the elongatemember. The hook element has a second rib-forcing surface adjacent thehook element's second end. The first end of the slender element joinsthe balance bar via a rotatable joint having a rotational axis that isvertical with respect to a plane of a patient's skin allowing thedescender post to rotate to extend the hook element under a rib.

In another embodiment, the descender post is substantially curved, andthe first rib-forcing surface projects a distance radially out from thevertical axis, thereby defining a moment arm reaching out from thevertical axis to the first rib-forcing surface. Thus when a rib bears onthe first rib-forcing surface, the descender post has a moment thatwould make the descender post rotate about the vertical axis.

In another embodiment, the curved descender post can rotate around thevertical axis by 90 degrees.

In another embodiment, a tissue engager possessing a balancing assemblyhas an elastic element that provides elastic recoil to return thebalancing assembly to its original configuration after deformation by aload.

In another embodiment, the elastic element is associated with the firstjoint axis.

In another embodiment, the elastic element is associated with the secondjoint element.

In another embodiment, the elastic element is associated with the thirdjoint element.

In another embodiment, all components of a self-balancing tissue engagerare substantially encompassed by an elastic sheath.

In another embodiment, the elastic element of the tissue engager has aYoung's modulus between 0.1 MPa and 60 MPa to permit retaining apreferred positioning of the elements of a self-balancing tissue engagerand recovering that preferred positioning of the elements.

In another embodiment an elastic element is spatially associated withthe gap region and provides a padded surface to the patient's tissues.

A method for retracting thoracic tissue, comprising retracting thoracictissue in the direction of a linear drive element by moving along thelinear drive element at least one of two arms that are orientedsubstantially perpendicular to the direction of retraction whileself-balancing tissue engagers automatically balance the forces amongstfour descending posts that are pushing on a rib.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate two tests of a biological sampledemonstrating the biomechanical phenomena of force relaxation and creep,respectively;

FIG. 2 is a diagram of a prior art retraction device;

FIG. 3 is a diagram of one embodiment of a device for separatinganatomical elements using a spring that exerts substantially constantforce on the anatomical elements;

FIG. 4 is a diagram of another embodiment of a device for separatinganatomical elements using a spring attached to a moveable drive blockthat exerts substantially constant force on the anatomical elements;

FIG. 5 is a diagram of another embodiment of a device for separatinganatomical elements using a spring attached to a moveable drive blockthat exerts substantially constant force on the anatomical elements,wherein the device also includes an adjustable indicator that is used toadjust the force exerted by the spring and a mechanical stop to limitthe range of motion of a retraction element;

FIG. 6 is a diagram of another embodiment of a device for separatinganatomical elements using a pneumatic cylinder to exert a substantiallyconstant force, where in a pressure reservoir can be used to keep thepressure in the pneumatic cylinder substantially constant as thecylinder expands, and wherein a pump can be used to keep the pressure inthe reservoir nearly constant;

FIG. 7 is a diagram of another embodiment a device for separatinganatomical elements using a motor to exert a substantially constantforce, wherein the electrical current driving the motor is keptsubstantially constant to keep the force substantially constant;

FIG. 8 is a diagram of another embodiment of a device for separatinganatomical elements using a motor to exert a substantially constantforce, wherein a force measuring device is used to determine the force,and a feedback loop is used to control the motor such that the force issubstantially constant;

FIG. 9 is a diagram of another embodiment of a device for separatinganatomical elements using a motor to exert a substantially constantforce which includes an alternate means for mechanical coupling of themotor;

FIG. 10 is a diagram of another embodiment of a device for separatinganatomical elements with an alternate configuration using more than oneretraction element and also using a visual indicator of the motion ofthe retraction elements;

FIGS. 11A and 11B illustrate exemplary time/displacement trajectoriesfor retraction with oscillating loading;

FIG. 12 illustrates a prototype motorized retractor utilizing abi-directional lead screw and that measures force on both retractorblades and separation of the blades;

FIG. 13 illustrates a force/time trace for a thoracotomy performed withthe prototype motorized retractor of FIG. 12;

FIGS. 14A and 14B show acceleration of force relaxation during bouts ofoscillating loading;

FIG. 15 shows a retraction for a thoracotomy in which oscillatingloading is periodically applied;

FIG. 16 shows an example of a Finochietto thoracic retractor in theprior art;

FIG. 17 shows a thoracic retractor of the prior art with a standardhand-cranked rack-and-pinion and a thoracic retractor in which the handcrank is replaced with a motor;

FIG. 18 shows a thoracic retractor driven by a computer controlled motoron a ball screw;

FIG. 19 shows a thoracic retractor driven by a hydraulic cylinder;

FIG. 20 shows a thoracic retractor having two actuators, a firsthand-driven actuator drives apart the arms of the retractor, and asecond motorized retractor that drives oscillating motion;

FIG. 21 illustrates a thoracic retractor having a first hand-drivenactuator that drives apart the arms of the retractor and a secondhydraulically driven pressure pad used to drive oscillating motion;

FIG. 22 shows a thoracic retractor having a first hand-driven actuatorthat drives apart the arms of the retractor and a second voice coilactuator used to drive oscillating motion;

FIG. 23 shows a retractor having multiple arms and actuators that applyoscillating loads;

FIG. 24 shows a retractor having multiple pairs of arms and actuators,wherein one actuator separates the pairs of arms, while actuators oneach arm drive oscillating motion;

FIG. 25 shows an angioplasty system for dilating tissues with anoscillating motion;

FIG. 26 shows another angioplasty system with an oscillating motion;

FIGS. 27A through 27C illustrates an angioplasty system with twocompartments to generate oscillating motions having higher frequencies;

FIGS. 28A and 28B show another angioplasty system with two compartmentsto generate oscillating motions having higher frequencies;

FIGS. 29A and 29B show another angioplasty system in which allcomponents are contained in a single compartment to permit oscillatingmotions having higher frequencies;

FIGS. 30A and 30B show another angioplasty system in which oscillatingmotions are driven by a thermally expanded bubble;

FIG. 31 illustrates how the time constant can be determined for forcerelaxation;

FIG. 32 illustrates how effective stiffness can be compared forsequential cycles of an oscillating loading;

FIG. 33 depicts an example retractors in the prior art;

FIG. 34 illustrates the retractor of FIG. 33 fitted with a set ofcalipers for measuring the separation of retraction elements and withstrain gauges for measuring the forces on each of the blades of theretraction elements;

FIG. 35 shows a prototype retractor having a motorized drive, a linearpotentiometer for measuring the separation of the retraction elements,and strain gauges for measuring the forces on each of the blades of theretraction elements;

FIG. 36 shows force and displacement with respect to time for aretraction during an experimental thoracotomy on a pig carcass;

FIG. 37 shows force and displacement with respect to time for aretraction during an experiment thoracotomy on a pig using aFinochietto-style retractor;

FIGS. 38A through 38C shows force and displacement with respect to timefor a second retraction during another experimental thoracotomy on a pigcarcass, wherein a larger break and two smaller breaks occurred duringthis retraction and two force events and a slope event preceded thelarger break;

FIG. 39 shows the force and the slope of the force in an expanded viewof the retraction in FIG. 38. This shows how examination of the slopeprovides a clearer signal of the slope and force events;

FIGS. 40A and 40B illustrate the force and the slope of the force overtime for a third retraction during another experimental thoracotomy on apig carcass;

FIGS. 41A and 41B illustrate the force and a second time derivative ofthe force (d2F/dt2) for two experimental retractions;

FIG. 42 shows an algorithm for detecting an imminent tissue fracture andpausing retraction in response;

FIG. 43 shows how acoustic events during retraction can occur over timeduring a retraction and how they can be used as predictors of tissuefracture;

FIG. 44 shows an example of a Finochietto thoracic retractor in theprior art;

FIGS. 45A and 45B show an experimental thoracic retractor in the priorart;

FIG. 46 show the orientations and motions of a swingletree and theforces on the swingletree;

FIG. 47 shows the orientations and motions of a doubletree and theforces on the doubletree;

FIGS. 48A and 48B shows an example of the prior art in which aderrick-like arm suspends a swingletree over an incision;

FIGS. 49A, 49B.1 and 49B.2 show the use of a balancing assembly in athoracic retractor having multiple retractor blades;

FIGS. 50A through 50C show how a balancing assembly can be adjusted toprovide any ratio of forces on multiple retractor blades;

FIG. 51 shows a balancing assembly having multiple tiers of balancebars;

FIG. 52 shows a balancing assembly having a number of blades that is nota multiple of 2;

FIG. 53 shows a retractor having a cable that permits a balance bar torotate;

FIG. 54 shows a balancing assembly having multiple tiers, with each tierfree to rotate;

FIGS. 55A through 55C show top, side, and front views, respectively, ofa balance assembly used for retracting a rib, wherein hooks that descendfrom the balance bars engage the rib;

FIGS. 56A through 56C shows top, side, and front views, respectively, ofa balance assembly used for retracting a rib, wherein hooks that descendfrom the balance bars engage the rib and an articulation in the balancebar permits the hooks to orient to the curvature of the rib;

FIG. 57 shows a thoracic retractor with a balancing assembly, whereinthe arms of the retractor has articulations;

FIG. 58 shows a balancing assembly in which balance bars overlap;

FIGS. 59A through 59E shows another embodiment of a retractor havingarticulations in the arms, retraction hooks to engage the tissues, andcables to provide automatic force balancing on the hooks;

FIGS. 60A and 60B show the embodiment depicted in FIGS. 59A through 59E,but as part of a retractor driven on a dual-thrust lead screw;

FIG. 61 shows another embodiment of a retractor using hydrauliccylinders to provide automatic force balancing on multiple retractorblades;

FIG. 62 shows another embodiment in which hydraulic cylinders provideautomatic force balancing for multiple retraction hooks;

FIGS. 63A through 63E show another embodiment in which fenestrated barson a fulcrum provide automatic force balancing for multiple retractionhooks;

FIG. 64 show another embodiment in which pivots are used to provideadjustable pivot points for swingletrees;

FIG. 65A through 65C show side views of the assembly in FIG. 64.

FIGS. 66A and 66B show another embodiment in which pivots are used toprovide adjustable pivot points for swingletrees;

FIG. 67 shows an example of a thoracic retractor in the prior art usedin a thoracotomy;

FIGS. 68A and 68B show examples of retractors in the prior art;

FIG. 69 diagrams the forces thought to act on the opposing blades of aretractor;

FIGS. 70A through 70D show additional examples of the prior art in whichcurved blades or swiveling joints permit accommodation to forces ofretraction;

FIG. 71 shows a more complete accounting of the forces and torques on aretractor;

FIG. 72 shows data from an experimental thoracotomy showing that theforce is not equal on two opposing blades of a retractor;

FIG. 73 shows an embodiment in which the retraction units are driven bya dual-thrust lead screw;

FIG. 74 shows another embodiment in which the retraction units aredriven by a dual-thrust lead screw, demonstrating rotational freedom ofthe arms;

FIGS. 75 shows side and end views, respectively, of an embodiment of aretractor drive mechanism comprising a roller drive with a shaft havingrectangular cross-section;

FIG. 76 shows how torques on the arms of a retractor increases forces onthe drive rollers of a roller drive;

FIG. 77 shows a roller drive with a circular shaft and how alignment ofthe rollers with respect to the circular shaft drives rotation andtranslation of the shaft;

FIG. 78 illustrates multiple views of a roller drive with a circularshaft depicting how varying the alignment of the rollers with respect tothe circular shaft provides variable control of shaft rotation andtranslation;

FIG. 79 shows another embodiment of a retractor using a roller drivewith a circular shaft;

FIG. 80 shows a another n embodiment of a retractor having dovetailjoints to permit additional motions of the retractor arms;

FIG. 81 shows another embodiment of a retractor arm having two dovetailjoints to permit additional motions of the retractor arms;

FIGS. 82A and 82B shows another embodiment of a retractor having twodual-thrust lead screws permitting an additional degree of freedom ofmotion;

FIG. 83 shows another embodiment of a retractor for thoracotomycomprising retractor blades pulled by straps attached to a patient;

FIG. 84 shows another embodiment of a retractor for sternotomycomprising retractor blades pulled by two ends of a strap that wrapsaround a patient;

FIG. 85 shows another embodiment of a retractor for sternotomycomprising retractor blades pulled by the two ends of a strap that wrapsaround a patient and inflatable balloons for generating tension;

FIG. 86 shows an example of a Weitland retractor in the prior art forretracting skin inserted into an incision in the skin;

FIG. 87 shows another embodiment of a retractor comprising retractorblades pulled by straps that wrap around the patient's wrist and havingpull tabs for generating retraction forces;

FIGS. 88A and 88B shows the anatomy of a chest wall around an incisionfor a thoracotomy;

FIG. 89 shows the deformation of the tissues of the chest wall byretractor blades during a thoracotomy;

FIG. 90 shows pinch points generated by retractor blades on the ribs andneurovascular bundle during a thoracotomy;

FIG. 91 shows regions of potential damage to tissues caused by elevatedtissue pressure during thoracotomy;

FIGS. 92A through 92C show an embodiment of a tissue engaging elementcomprising posts placed into holes drilled into adjacent ribs;

FIG. 93 shows another embodiment of a retractor comprising posts thatengage the arms of the retractor;

FIGS. 94A and 94B show another embodiment of a retractor comprisingclips that grasp the ribs and attach to the arms of a retractor;

FIGS. 95A and 95B show embodiments of retractor clips having one or twospikes, respectively, for engaging the ribs;

FIG. 96 shows a top view of another embodiment of a retractor comprisingtwo retractor arms and multiple clips for engaging the ribs for athoracotomy;

FIGS. 97A through 97D show the top and side views of another embodimentof a retractor comprising two retractor arms having descender posts forengaging ribs, and two side views of a descender posts having hooks androtatable mounts;

FIGS. 98A and 98B show another embodiment of a descender post comprisinga hook engaged with the retractor arm via a rotatable mount;

FIG. 99 shows a 3D model of a retractor having descender posts withhooks rotatably mounted on retractor arms;

FIG. 100 shows another embodiment of a retractor arm comprising an armand a plurality of descender posts for engaging a rib;

FIGS. 101A through 101E shows another embodiment of a descender postcomprising a projection that projects laterally from the descender postand terminates in a tip having one of several configurations;

FIG. 102 shows another embodiment of a retractor comprising tworetractor arms each having a first and a second descender post forengaging a rib;

FIG. 103 shows another embodiment of a retractor comprising multiplearms, each having descender posts and configured to engage multiple ribson each side of a thoracotomy incision;

FIGS. 104A through 104C shows another embodiment of a descender postcomprising a post with clips on one end, wherein the clips close on arib when pushed against the rib;

FIGS. 105A and 105B show the deformations under loading of a thoracicretractor in the prior art;

FIG. 106 shows an embodiment comprising a retractor having two opposingblades, a servo-motor, a servo-controller, and linear potentiometer;

FIG. 107 shows an algorithm in which force on the retractor is used todetermine and correct for deformation of the retractor when loaded;

FIG. 108 shows an embodiment of a device for compensating for changes inretractor deformation comprising a force measuring device, aforce-to-deformation translator, a servo-controller and a servo-motor;

FIG. 109 shows an embodiment of a device for compensating for changes inretractor deformation comprising a force measuring device, aforce-to-deformation translator, a servo-controller and a servo-motor inwhich all components fit onto one arm of the retractor;

FIG. 110 shows an embodiment of a thoracic retractor;

FIG. 111 shows an embodiment of a retraction driver;

FIG. 112 shows an embodiment of a retractor arm assembly for athoracotomy;

FIG. 113 shows an enlarged view of a rotatable mount on a thoracicretractor;

FIG. 114 shows the design of the balance arms of a retractor armassembly;

FIG. 115 shows an example of a user interface built into a thoracicretractor;

FIGS. 116A and 116B show force and displacement for two automatedthoracotomy retractions performed with a prototype thoracic retractor;and

FIGS. 117A through 117C show the force on a left arm and an EventDetection Signal for the automated retractions shown in FIGS. 116A and116B.

FIG. 118—A rib cage; inserted plane defines “profile” view.

FIGS. 119A through 119C—Profile view from a rib cage.

FIG. 120A—A thin Tissue Retraction Element in profile view.

FIG. 120B1—A Tissue Retraction Element with a square shape of the priorart.

FIG. 120B2—A Tissue Retraction Element with a polished surface.

FIG. 120C—A low-friction Tissue Retraction Element.

FIG. 120E—A bagged, lubricated Tissue Retraction Element.

FIG. 120F—A Tissue Retraction Element with lubricant applied in theoperating room.

FIG. 120G—A Tissue Retraction Element with water-activated lubricantcoating.

FIG. 120H—A Tissue Retraction Element with an elastic sheath.

FIG. 120I—A Tissue Retraction Element with elastic joints.

FIG. 121—A surgeon's finger, in section view.

FIG. 122—An Articulated Safety Finger, in section view.

FIG. 123—An Articulated Safety Finger, straight for insertion.

FIG. 124A—An Articulated Safety Finger, pulling on cable.

FIG. 124B—An Articulated Safety Finger, flexed.

FIG. 125—Articulated Safety Finger, ready for retraction.

FIGS. 126A through 126C—Surgeon hand-actuating the ASF's Finger FlexingLever.

FIG. 127—Detail of the ASF's Finger Flexing Lever.

FIG. 128—Detail showing the action of the ASF's Finger Flexing Lever.

FIG. 129—Oblique view of Swinging Safety Finger TRE.

FIG. 130A—Profile view of Swinging Safety Finger closed and thin forinsertion.

FIG. 130B—Profile view of Swinging Safety Finger opened and retractingtissue.

FIG. 131—Swinging Safety Finger showing off-center deep area creatingmoment.

FIGS. 132 A through 132C—Deployment sequence of the Swinging SafetyFinger.

FIGS. 133A through 133F—Time-stepped views showing gradually changingprofile of SSF showing three steps viewed from the side and same threesteps viewed from above.

FIG. 134 shows how the gap accommodates many rib rotations and sizes toalways protect the neurovascular bundle.

FIG. 135 shows a swinging safety finger with a rib resting onit.

FIGS. 136A through 136C shows a helical retraction element thatself-engages on insertion.

FIG. 137 shows a prototype automated retractor for thoracotomy.

FIG. 138 shows a retractor with tissue engagers having balancing beamsand descender posts to retract ribs for thoracotomy.

FIG. 139 shows a self-balancing tissue engager for retracting ribs.

FIG. 140 shows a descender post engaging a rib for retraction.

FIG. 141 shows a photograph from a thoracotomy on a pig showing the gap.

DETAILED DESCRIPTION A. Constant Force (Creep)

Many biological materials are viscoelastic, so they exhibittime-dependent mechanical properties (Wainwright et al., 1976,Mechanical Design in Organisms, John Wiley & Sons; Woo et al., 1999,Animal Models in Orthopaedic Research, CRC Press. pp. 175-96; Provenzanoet al., 2001, Ann. Biomed. Eng. 29:908; Vanderby and Provenzano, 2003,J. Biomech. 10:1523; Yin and Elliott, 2004, J. Biomech. 37:907). Tosimplify this discussion, consider the force (the stress) required tostretch a sample of biological material. Consider FIG. 1A whichillustrates test on a sample A200 of a biological material whereby thesample A200 is stretched by an instrument has a stationary unit A202that measures force and a moving unit A204 that measures displacementwhile stretching a sample. The sample A200 is initially stretched byhaving the moving unit A204 move away from the stationary unit A204. Thestationary unit A204 then remains at a fixed position, holding thesample A200 at constant deformation. Over time, the measured forcedecreases. This is an example of “force relaxation” or “stressrelaxation”. FIG. 1B shows a similar test on sample A200. Initially, thesample A200 is stretched; however, now moving unit A204 moves such thata constant force is applied to sample A200, and now the sample A200stretches longer over time, a phenomenon known as “creep”. Forcerelaxation and creep occur when retracting an incision. The deformationsof the tissues around the incision are more complex than the simplestretch shown in FIGS. 1A and 1B, but the tissues, nevertheless, exhibitforce relaxation and creep.

Standard practice during a sternotomy or thoracotomy is to spread theribs slowly to a few centimeters, hold for a minute or so (allowingstress relaxation), and then slowly open over several minutes (allowingcontinued viscous deformation/stress relaxation) to the final opening.

The time dependent behavior of biological tissues has been specificallyconsidered in the design of some retraction devices. U.S. Pat. No.4,899,761 to Brown and Holmes discloses a distractor for separatingvertebrae to measure spinal instability. The distractor of Brown andHolmes uses constant velocity deformation to standardize measurements ofthe mechanical properties of the motion segment of a spine to diagnosewhether surgical intervention is necessary. Additionally, US PatentApplication Publication No. 2006/0025656 to Buckner and Bolotindiscloses stress relaxation as a means of reducing force duringretraction.

Creep has not been considered in the design of retraction devices.However, application of a constant force ensures that (a) anunexpectedly or inappropriately large force is applied as would be thecase for manual or motor driven retraction devices, and (b) viscoelasticdeformation is allowed to proceed, thereby reducing the loads onanatomical elements that might rupture.

Different embodiments are disclosed, with reference to the figures, ofassemblies and devices that apply a substantially constant force to oneor more anatomical elements to move the anatomical elements. Not allembodiments of the invention are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure satisfies applicable legalrequirements.

FIG. 2 illustrates a retraction device in the prior art. Retractor A2 isa mechanical device utilizing two opposed retraction elements A6, A8.Each retraction element A6, A8 has a blade A4 that is inserted into anincision, each blade A4 engaging one side of an incision. One retractionelement A8 is moveable with respect to the other retraction element A6,with motion being driven by a rack-and-pinion drive A10 that is manuallydriven with a drive handle A12. The retraction elements A6, A8 exert aforce on the anatomical elements on either side of the incision toseparate the anatomical elements, thereby opening the incision. Alimitation of this device is that the force can vary dramatically withsmall displacements, thus an operator might exert an inappropriate forcewhile attempting to move the retraction elements A6, A8 only a smalldistance.

FIG. 3 illustrates an embodiment of the present invention which isdesigned to apply a constant force. It is a mechanical device utilizingtwo opposed retraction elements A16 and A18. Each retraction elementA16, A18 has a blade A14 (similar to blade A4) that is inserted into anincision, each blade A14 engaging one side of the incision. Oneretraction element A16 is moveable with respect to the other retractionelement A18 and is mounted on a sliding carriage A20. The slidingcarriage A20 is driven by a spring A26 that exerts a substantiallyconstant force over the range of motion such that the force exerted bythe opposing retraction elements A16, A18 on the anatomical elements issubstantially constant. The spring A26 is connected to a moveable anchorblock A22 that allows an operator to adjust the stretch of the springA26 and, thereby, the force exerted by the spring A26 on the anatomicalelement via the sliding carriage A20. The moveable anchor block A22 hasa lock screw A24 to secure the position of moveable anchor block A22after adjustment. Thus, the spring A26 serves to exert a substantiallyconstant force, and this force cannot be accidentally exceeded by, forexample, attempting to move the retraction elements A16 and A18 a smalldistance. Furthermore, if the spring A26 does not have a large springconstant, then the distance from the sliding carriage A20 to themoveable anchor block A22 can be sufficiently large that small errors inadjustment of this distance do not introduce large errors in the force.

FIG. 4 illustrates another embodiment of the present invention which isdesigned to apply a substantially constant force that is larger thanthat depicted in FIG. 3. It is a mechanical device utilizing two opposedretraction elements A30, A32. Each retraction element A30, A32 has ablade A28 (similar to blade A4) that is inserted into an incision, eachblade A28 engaging one side of the incision. One retraction element A30is moveable with respect to the other A32, being mounted on a slidingcarriage A34. The sliding carriage A34 is driven by a spring A39 thatexerts a substantially constant force over the range of motion such thatthe force exerted by the opposing retraction elements A30 and A32 on theanatomical elements is substantially constant. The spring A39 isconnected to a driven anchor block A36 that allows an operator to adjustthe stretch of the spring A39 and, thereby, the force exerted by thespring A39 on the anatomical element via the sliding carriage A34. Thedriven anchor block A36 has a manual drive mechanism, such as a ratchetor a rack-and-pinion, driven by a handle A38 for manual drive and,optionally, a lock screw to secure the position of the driven anchorblock A36 after adjustment.

FIG. 5 illustrates another embodiment of the present invention thatprovides an indicator of the force exerted on the tissue. It is amechanical device utilizing two opposed retraction elements A42, A44.Each retraction element A42, A44 has a blade A40 (similar to blade A4)that is inserted into an incision, each blade A40 engaging one side ofthe incision. One retraction element A42 is moveable with respect to theother retraction element A44, and is mounted on a sliding carriage A46.The sliding carriage A46 is driven by a spring A54 that exerts asubstantially constant force over the range of motion such that theforce exerted by the opposing retraction elements A42, A44 on theanatomical elements is substantially constant. The spring A54 isconnected to a driven anchor block A48 that allows an operator to adjustthe stretch of the spring A54 and, thereby, the force exerted by thespring A54 on the anatomical element via the sliding carriage A46. Thedriven anchor block A48 has a manual drive mechanism, such as a ratchetor a rack-and-pinion drive, driven by a handle A50 for manual drive and,optionally, a lock screw to secure the position of the driven anchorblock A48 after adjustment. There is also a force indicator A60 that isa graduated rod, with graduations indicating force exerted by the springA54 for the indicated stretch, that is used to indicate where to placethe driven anchor block A48 or whether the driven anchor block A48should be moved to maintain appropriate stretch of the spring A54 tomaintain a substantially constant force on the moveable retractionelement A42. The position of the force indicator A60 is secured by anindicator set screw A52. There is also a mechanical stop A56 with itsposition secured by the stop set screw A58 such that the motion of thesliding carriage A46 cannot exceed a predetermined motion.

FIG. 6 illustrates another embodiment of the present invention that usesa pneumatic piston to exert a substantially constant force. It is amechanical device utilizing two opposed retraction elements A64, A66.Each retraction element A64, A66 has a blade A62 (similar to blade A4)that is inserted into an incision, each blade A62 engaging one side ofthe incision. One retraction element A64 is moveable with respect to theother retraction element A66, and is mounted on a sliding carriage A68.The sliding carriage A68 is driven by a pneumatic piston A74 that exertsa substantially constant force over the range of motion such that theforce exerted by the opposing retraction elements A64, A66 on theanatomical elements is substantially constant. The piston A74 isconnected to a pressure reservoir A80 by a pressure hose A76. Thepressure reservoir A80 has sufficient volume of gas such that changes inthe volume of the piston A74 as the piston A74 moves do not introducelarge changes in the pressure. The pressure reservoir A80 can be fittedwith a pressure gage A78 that allows an operator to observe thepressure. The pressure reservoir A80 can be connected to a pressure pumpA86 that permits an operator to increase the pressure in the reservoirboth to initiate the force at the piston A74 or to prevent pressure fromdropping in the pressure reservoir A80 should the motion of the pistonA74 be too large, causing a drop in pressure, or to allow the piston A74to change from a first substantially constant force to a secondsubstantially constant force. The pressure reservoir A80 also can have ableed valve A82 that allows an operator to reduce the pressure, torelease the pressure, or to move from a first substantially constantforce to a second substantially constant force. Additionally, there canbe a mechanical stop A70 with its position secured by a stop set screwA72 such that the motion of the sliding carriage A68 cannot exceed apredetermined motion.

FIG. 7 illustrates another embodiment of the present invention whichutilizes a motorized drive to exert a substantially constant force. Itis a mechanical device utilizing two opposed retraction elements A90,A92. Each retraction element A90, A92 has a blade A88 (similar to bladeA4) that is inserted into an incision, each blade A88 engaging one sideof the incision. One retraction element A90 is moveable with respect tothe other retraction element A92, and is mounted on a sliding carriageA94. The sliding carriage A94 is driven by a motor A96 that exerts asubstantially constant force over the range of motion such that theforce exerted by the opposing retraction elements A90, A92 on theanatomical elements is substantially constant. The motor A96 isconnected by an electrical cable A98 to a motor controller (not shown).The motor controller ensures that the torque generated by the motor A96is substantially constant such that the force exerted by the opposingretraction elements A90, A92 on the anatomical elements is substantiallyconstant.

FIG. 8 illustrates another embodiment of the present invention whichutilizes a feedback system to exert a substantially constant force. Itis a mechanical device utilizing two opposed retraction elements A102,A104. Each retraction element A102, A104 has a blade A100 (similar toblade A4) that is inserted into an incision, each blade A100 engagingone side of the incision. One retraction element A102 is moveable withrespect to the other A104 and is mounted on a sliding carriage A106. Thesliding carriage A106 is driven by a motor A111 that exerts asubstantially constant force over the range of motion such that theforce exerted by the opposing retraction elements A102, A104 on theanatomical elements is substantially constant. The motor A111 isconnected by an electrical cable A108 to a motor controller A114. Aforce measuring device A110 is attached to the retraction element A104(or optionally to retraction element A102) such that the force measuringdevice A110 determines the force exerted by the retraction element A104on the anatomical element. The force measuring device A110 is connectedto the motor controller A114 via a signal cable A112 such that the forceis transmitted as a signal to the motor controller A114. The motorcontroller A114 implements a feedback loop such that the force measuredby the force measuring device A110 is substantially constant such thatthe force exerted by the opposing retraction elements A102, A104 on theanatomical elements is substantially constant. Motor controller A114can, optionally, be connected to another device (not shown) by cableA116 to, for example, provide additional processing abilities or toprovide a display of force.

FIG. 9 illustrates another embodiment of the present invention that issimilar to that disclosed in FIG. 7 but in which a motor A124 is mounteddifferently. Motor A124 is directly attached to retractor element A120by mount A126, and retractor element A122 is directly attached to thelinear drive shaft A127. This permits use of a differently configuredmotor, possibly with integrated motor controller (not shown) orconnected by a cable A128.

FIG. 10 illustrates another embodiment of the present invention which isa mechanical device utilizing multiple moveable retraction elementsA132, A134 that are mounted on a frame A130. Each moveable retractionelement A132, A134 can be independently moved. The various mechanismsdescribed in FIGS. 3 through 9 for exerting a substantially constantforce via the blades A138 (examples of blades include curved or bentblades that extend into the incision) of retraction elements can beimplemented for each of these moveable retraction elements A132, A134.The mechanisms can be implemented such that the force exerted by eachindividual moveable retraction element A132, A134 is independent of theforce exerted by any other moveable retraction element A132, A134.Optionally, position measuring devices (not shown, examples includelinear potentiometers, LVDTs, optical encoders) can be placed on eachmoveable retraction element A132 and A134 such that an independentmeasure of position is determined and displayed on a visual positionindicator A136 on the frame A130. Alternatively, the force exerted byblades A138 of retraction elements A132, A134 on their respectiveanatomical elements can be measured by a force measuring device (notshown, examples include appropriately placed strain gauges), and theforces displayed on indicators (not shown) also on the frame A130. Anelectrical cable A137 can be used to provide power to electrical deviceson the frame A130 and to convey electrical signals from electricaldevices on the frame A130 or elsewhere on the retractor to a separatemotor controller (not shown) or computer (not shown).

B. Oscillating Loading

Deformation of biological materials during the first phase of retractionis usually done one-directionally—the deformation pushes anatomicalelements apart (e.g., thoracotomy) or stretches arteries open (e.g.,angioplasty). The direction of motion during deformation is rarelyreversed and then only to correct for errors, such as to reposition arib retractor that has slipped or to free a blood vessel that hasaccidentally been captured under a retractor blade.

Trauma to the displaced tissue is a common consequence of thesedeformations. Ribs fracture during thoracotomy, costosternal jointsdislocate during sternotomy, muscles tear during retraction, and bloodvessel walls rip during angioplasty. Even for those deformations used tochange anatomical position or shape, damage to the tissue can be largerthan desired; for example, a fibrous capsule might tear when stretchingis preferred.

Many biological materials are viscoelastic, so they exhibittime-dependent mechanical properties (Wainwright, Biggs et al. 1976;Woo, Manson et al. 1999; Provenzano, Lakes et al. 2001; Vanderby andProvenzano 2003; Yin and Elliott 2004; Erdogan, Erdogan et al. 2005).

One behavior of biological complex materials that has not beenconsidered in the design of retractors is “work” or “stress” softening.Work softening is evident during cyclic loading/unloading and ischaracterized as a reduction in the force at a given deformation duringsuccessive cycles, relative to the initial loading. Viscoelasticmaterials exhibit stress softening, but the initial stiffness recoverswith rest for most non-biological viscoelastic materials (e.g. filledrubbers). For many biological materials, initial stiffness is notrecovered, reflecting changes in the non-viscous components of thematerial, thought to arise from the irreversible dislocation ofcomponents (such as the unentanglement of tangled polymers), fromplastic deformation of polymeric components, or from failure ofmicroscopic components (such as the fracture of single molecules). Theunderlying phenomenology of stress softening is not well understood(Horgan, Ogden et al. 2004), especially for biological materials(Vincent 1975; Weisman, Pope et al. 1980; Fleck and Eifler 2003; Kirton,Taberner et al. 2004; Kirton, Taberner et al. 2004; Speich, Borgsmilleret al. 2005; Chaudhuri, Parekh et al. 2007; Dorfmann, Trimmer et al.2007). Nevertheless, the generally observed phenomenon of worksoftening, or any change in material property when subjected tooscillating loading, can be exploited.

Thus, an alternate means of deforming tissue, relative to traditionalunidirectional loading, is to cyclically load the tissue. For example,the blades of a retractor move forward and backward, or an angioplastyballoon cyclically inflates and deflates.

Oscillatory motion provides at least three benefits. First, it can “worksoften” the material, decreasing the forces required to achieve adeformation. Second, oscillatory motion can be used to measure theviscoelastic parameters of the material (elastic and viscous moduli),and the results of these measurements can optionally be used to guideadditional manipulations of the tissue. Third, a large number of smalldeformations in series can lead to small scale failure of componentsthus avoiding catastrophic failure of the entire structure—similar tothe release of energy at a geologic fault line by many small tremors asopposed to one large earthquake.

Note that oscillation can be at different frequencies. A frequency sweepcan be used to identify a harmonic. “White noise” can be used in dynamicanalysis to determine multiple resonant frequencies that can arise fromthe composite nature of biological materials. Oscillation can beconducted at two different frequencies, either one following the otheror with both frequencies superimposed, to act upon different componentsof the composite material comprising the tissue. For example, a lowerfrequency can be used to work soften a ligament and a higher frequencycan be used to work soften a polymer by vibrating the molecules in thepolymer. These frequencies can be fractions of a Hertz to a megaHertz.Thus, oscillations can include mechanical vibrations, acousticvibrations, ultrasound, and any other reciprocating motion.

B.1 Reduction of the Force of Retraction & Reducing Catastrophic FailureB.1.1 Tissue Spreaders and Retractors

Oscillatory motion of a spreader or retractor can be generated in manydifferent ways, depending on the necessary frequency and amplitude ofactuation, which when coupled with the force of retraction and the massof the oscillating system (retractor blade and tissue) determine thepower requirements for the motor or other actuator.

For the following discussion, two motions are defined:

-   -   1. the retraction motion, which is the overall, or average,        motion during the first phase of retraction that is used to        achieve the final deformation of the tissue; and    -   2. the oscillation motion, which is a motion that is        superimposed on the retraction motion.

As shown in FIG. 11A, the two motions can be performed separately intime, with a retraction motion B4 proceeding to a given separation andthen pausing, followed by an oscillation motion B2. Alternatively, asshown in FIG. 11B, the retraction motion B4 and the oscillation motionB2 can be superimposed in time, thus the retraction motion B6 would be anear-zero frequency component of the motion, and the oscillation motionwould be the higher frequency component.

B.1.1.1 Experimental Results from Oscillating Loading of Tissues

B.1.1.1.1 An Example of a Retractor for Oscillating Motion

A retractor is shown in FIG. 12 that uses a bi-directional ball screwB10 (i.e., having two bearings that travel in opposite directions) thatis driven by a stepper motor B8, which here is an MDrive 23Plus made byIntelligent Motion Systems, Inc. The bi-directional ball screw B10 ismounted to a rail B14 with two linear translation stages B12, which hereare LWHG 25 made by IKO, such that each translation stage B12 attachesto one of the bearings of the bi-directional ball screw B10, thus whenthe bi-directional ball screw B10 is rotated by the motor B8, thetranslation stages B12 travel in opposite directions. A retractor armB18, fabricated by hand from mild steel angle iron that wascut/bent/welded into shape, is mounted to each translation stage B12.Each retractor arm B18 has a retractor blade B20 that is fabricated byhand with mild steel.

A linear potentiometer B16, which in this case is a 5 kOhm 100 mm madeby Schaevitz, is used to measure separation of the retractor blades B20.The static mount of the potentiometer B16 is affixed to the rail B14,and the piston of potentiometer B16 is affixed to one of the translationstages B12. Note that any means of measuring displacement can be usedhere, such as optical encoders, contact and non-contact proximitysensors, digital calipers, and the like.

The retractor blades B20 are instrumented with a full-bridge straingauge assembly which includes two (2) gauges, which in this case aremodel CEA-06-125UN-350 made by Vishay Micro-Measurements, on each sideof each retractor blade B20. The signal from the strain gauges is thenamplified by a signal conditioner (not shown) which in this case is aModel OM-2 from 1-800-LoadCells. Note that force can be measured by anyof several means, such as drive current on the motor (and other means ofmeasuring torque on the drive mechanism), fiber optic strain gauges,optical sensors of deformation, and the like.

All signals from the potentiometer B16 and the signalconditioners/strain gauges are read by a Windows-based computer using adata acquisition card, which in this case is a National InstrumentsModel USB-6211 and software, such as LabVIEW made by NationalInstruments, with software prepared by Katya Prince of PrinceConsulting.

The stepper motor B8 is controlled with IMS Terminal software, made bymade by Intelligent Motion Systems, Inc. Note that a servo-motor canalso be used.

The strain gauges were calibrated by hanging known weights from eachblade B20 of the retractor. The linear potentiometer B16 was calibratedwith a metric ruler.

B.1.1.1.2 Experiments

A series of experiments were conducted with the retractor presented inFIG. 12 using parts from pig cadavers. The parts were a “front quarter”purchased from Nahunta Pork Center (Pikeville, N.C.). A front quarter isbasically a whole pig cut at the waist (forming a front half) and splitdown the vertebrae (forming left and right quarters); thus, each quarterhad an intact rib cage (one side), spine (bisected), and shoulder. Allparts had been refrigerated after slaughter, used within 24 hours ofslaughter, and warmed by immersion in warm water (while wrapped in aplastic bag to prevent soaking of the tissue) to near body temperature(31° C. to 37° C.). The quarters ranged in size from 8 to 12 kg.

Thoracotomies were performed between three (3) to four (4) rib pairs oneach quarter, almost always performing an incision between ribs five (5)and six (6), seven (7) and eight (8), nine (9) and ten (10), and eleven(11) and twelve (12). Thoracotomies were performed by:

-   -   cutting the skin with a scalpel over the range of the        thoracotomy;    -   bisecting the muscles overlying the ribs with a scalpel;    -   cutting through the intercostal tissues with a scalpel;    -   pushing a finger between the ribs to make a small opening;    -   inserting the closed blades of the retractor into the opening;    -   positioning the retractor such that the blades sat just dorsal        of the midline and its axis of opening were parallel with the        midline; and    -   initiating opening according to a specified algorithm via        computer control of the stepper motor.

Incisions were typically 110 mm to 130 mm long, with longer incisionsbeing performed on larger quarters.

Experimental retractions with the retractor shown in FIG. 13 are thefirst simultaneous measurements of force and displacement duringthoracic retraction.

FIG. 13 shows the displacement B21 of the blades B20 (i.e., the distancebetween the blades B20), and force B22 on one blade B20 with respect totime for a “standard retraction”, similar to that defined by Bolotin etal. (Bolotin, Buckner et al. 2007), which proceeds as follows:

-   -   a first move, opening to 40 mm in one (1) minute (⅔ of final        opening),    -   pause 2 minutes for force relaxation,    -   a second move, opening to 60 mm in three (3) minutes (to the        final opening).

Thus, a total opening of 60 mm is reached in 6 minutes in this example.Retraction was of a fully automated—the computer controlled the motorB8, and the motor drove the blades B20 apart. Each of the two moves isconstant velocity (40 mm/min for the first and 6.8 mm/min for thesecond). This somewhat matches the pace described by thoracic surgeons,but there is no standard clinical practice. Surgeons use a proceduredefined by their training, personal experience, patient condition, andestimates of force applied at the handle of a hand-cranked retractor.Force relaxation, as described by Buckner and Bolotin (Buckner andBolotin 2006; Bolotin, Buckner et al. 2007) is evident during atwo-minute pause B23—the force required to maintain the 40 mm openingdecreases with time. The points on the force B22 marked with arrows B24mark significant tissue breaks, as evidenced by the change in theforce/time slope and by audible “snaps” during the retraction.

FIG. 14A shows a retraction in which the displacement B21 is shown bythe upper trace, and force B22 on one blade is shown by the lower trace.There are four small retractions B25 (2 mm each over 10 seconds,velocity=0.2 mm/s) of which the second two were followed by pauses B26of approximately 50 seconds and the first two were followed by pausesB27 of 50 seconds interrupted by oscillation motions B28. Theoscillation motions B28 were 11 Hz with one (1) mm amplitude, 400cycles, and given the high frequency of oscillation, they appear on thedisplacement trace as thickened regions of the trace. Force relaxationwas seen for each of the four pauses B26, B27, as evidenced by thedecrease in force that follows the onset of each pause. During eachoscillation motion B28, the force oscillated with each cycle ofopening/closing. Importantly, when the force minima are examined oversuccessive cycles, the force dropped rapidly.

FIG. 14B shows what the force/time curve looks like when only the forceminima are considered—there is an accelerated force relaxation (AFR)B30, during the oscillation motions B28, as illustrated by the greyregions in FIG. 14B. Thus, while the force declined during normal forcerelaxation (NFR) B32, as depicted during the two-minute pause in FIG. 13and during the 3rd and 4th pauses B26 in FIG. 14B, the force declinedmuch more rapidly during the AFR B30 (1st and 2nd pauses B27 of FIG.14B) than during the NFR B32. Also, the AFR B30 had a larger magnitudewhen the oscillation motion B28 was initiated earlier in the pause, asevidenced when the 2nd pause/oscillation motion B28 is compared to the1st pause/oscillation motion B28—the oscillation motion B28 startedsooner in the 2nd pause oscillation and a larger AFR B30 was seen.

FIG. 15 shows a retraction in which a different trajectory is followedthan for a standard retraction, which is called an “oscillatingretraction” for this discussion. Displacement, or separation of theblades B20, is shown by trace B36. Force on one blade B20 is shown bytrace B38. During the experiment depicted in FIG. 15, the incision wasopened and oscillated repeatedly. Three general features observed duringoscillating retractions like this are:

-   -   1. the retraction force does not peak as high as is seen during        the first opening of the standard clinical pace retraction        (compare to FIG. 13);    -   2. the maximum force during oscillating retraction is frequently        lower than the maximum force in a standard clinical pace        (compare to FIGS. 13); and    -   3. there are fewer large, obvious breaks during oscillating        retractions than during standard clinical pace retractions.

The latter point is shown in FIG. 13 where breaks B24 are marked witharrows B24—the breaks appear as rapid changes in the slope of theforce/time trace that are almost always accompanied by loud snaps orcracks. These events are common during standard retractions, especiallyin the final 20 seconds of the first, one-minute opening and during thelast two minutes of the second, three-minute opening. These rapidchanges in slope, accompanied by loud snaps or cracks, are almost neverseen/heard during oscillating retractions. This point is especiallyimportant in light of the tissue trauma that is frequently observedduring normal surgical practice—broken ribs, dislocated costo-chondraljoints, and torn ligaments and tendons (Vander Salm, Cutler et al. 1982;Greenwald, Baisden et al. 1983; Baisden, Greenwald et al. 1984;Woodring, Royer et al. 1985; Bolotin, Buckner et al. 2007; Lewis 2007).

Thus, there are several advantages conferred by oscillating retractions:

-   -   1. accelerated force relaxation rapidly decreases the force        required for opening;    -   2. the large peak in force seen during the first, one-minute        opening of a standard retraction is not evident;    -   3. the maximum force experienced during retraction is frequently        smaller during oscillating retraction; and    -   4. there are fewer, large tissue breaks during oscillating        retraction.        All of these advantages can result in reduced tissue trauma        during retraction.

B.1.1.2 Single-Actuator Retractors

FIG. 16 shows a Finochietto retractor in the prior art (similar toretractor A2 in FIG. 2). It has a fixed retraction element B44 attachedto a rack B45 of a rack-and-pinion drive B46. A moveable retractionelement B42 is attached to the rack and pinion drive B46 that drivesmotion B52 of the moveable retraction element when manual handle B48 isrotated. Each of the retraction elements B42, B44 has a single blade B40(similar to blade A4 in FIG. 2) that engages the tissue to be retracted.

One way to implement a retractor with both a retraction motion and anoscillation motion is to use a single actuator that drives both theretraction and the oscillation motions, such as the retractor shown inFIG. 12.

FIG. 17 shows another embodiment of a single actuator retractor, inwhich a motor B60 replaces the hand crank B48 of a typicalFinochietto-style rack-and-pinion retractor. The motor B60 can be anymotor appropriate for generating the desired motions B52, such as aservo-motor or a stepper motor. The instructions to the motor generateany desired motions for retraction motions as well as oscillations foroscillation motions. Thus, the retractor can perform retraction andoscillation motions that either are separated in time or aresuperimposed in time.

FIG. 18 shows another embodiment in which the rack-and-pinion drive B46is replaced with a lead screw B62 turned by a motor B74, either astepper motor or a servomotor. The motor B74 moves the moveableretraction element B70 with respect to fixed retraction element B72 toachieve the desired motion B68. Control of the motor B74 can be eitheron-board with the motor B74 or off-board connected by an electricalcable B76.

In yet another embodiment shown in FIG. 19, the rack-and-pinion driveB46 is replaced by a hydraulic cylinder B82. A pressure pump B94 isconnected to a pressure reservoir B88 by a pressure hose 92, and thepressure reservoir B88 is connected to the hydraulic cylinder B82 by apressure hose B84. Pressurization of the hydraulic fluid in the pressurepump B94 pressurizes the pressure reservoir B88 that feeds the hydrauliccylinder B82 which forces a moveable retraction element B78 and a fixedretraction element B80 apart. A pressure gauge B86 reports the pressurein the system, and a bleed valve B90 permits release of pressure.Oscillation of the pressure in the hydraulic fluid generates theoscillation motion. Oscillation can be driven by one of several means,such as a piston B85 attached to pressure reservoir B88 that is drivenin and out by motor B87.

B.1.1.3 Dual-Actuator Retractors

The retraction and oscillation motions can be generated by separateactuators. For example, a first actuator drives the retraction motion,and a second actuator drives the oscillation motion. This confersseveral advantages:

-   -   different actuators can be matched to the different power        requirements for the two different motions;    -   different actuators can be matched to the displacements required        for the two different motions; and    -   different distributions of masses are permitted, e.g. removing        bulky components required for the large amplitude motions of the        retraction motion from the components that must be driven at        higher frequency but lower amplitude for the oscillation        motions.

In one embodiment shown in FIG. 20, a retraction motion is generated bya first actuator which in this example is a rack-and-pinion drive B98driven by hand crank B99 along a rack B100 on a conventionalFinochietto-style retractor. The first actuator moves a moveableretraction element B101. The oscillation motion B102 is generated by amotor-driven acentrically mounted cam B104 that rides on two surfaces, afirst surface B106 attached to the rack B100 of the retractor and asecond surface B107 attached to an oscillation motion element B108 thatis mounted to the rack B100 by a hinge B109. When the acentricallymounted cam B104 rotates, the oscillation motion element B108 oscillateswith motion B102 with the frequency of rotation of the motor and withamplitude determined by the diameter and acentricity of the cam B104 andthe lever-arm of the oscillation motion element B108.

In another embodiment shown in FIG. 21, a hand-cranked rack-and-piniondrive B110 is used for performing the retraction motion. A secondactuator B112 drives the oscillation motion. The second actuator B112presented here is a thin hydraulic cylinder or pressure pad B120 mountedon each retractor blade B114 and is driven by a hydraulic system capableof generating the necessary pressures and volumes to drive the requisitemotion. In this example, a pressure hose B124 attached to pressure padsB120 and to an external pressure source (not shown) permits cyclicoscillation of the pressure pads B120 via an oscillating flow B126 offluid. The second actuator B112 could be any actuator that mounts to theretractor blades B114 of retraction elements B116, B118, such as a voicecoil, a linear motor, a hydraulic cylinder or other actuator capable ofgenerating the oscillation motion. A semi-transparent view of aretractor blade 114 is provided to allow a more complete view of theassembly.

In another embodiment shown in FIG. 22, a retractor has a motorized leadscrew drive B130 that drives along the lead screw B132 for theretraction motion. Voice coils B134 mounted onto blades B136 of theretraction elements drive an oscillation motion B138.

B.1.1.4 Multiple-Actuator Retractors

FIG. 23 shows an embodiment in which a retractor B140 with multiple armsand actuators can apply oscillating loads. The retractor B140 has aframe B142 to which independent actuators B144 and arms with attachedblades B146 are mounted. The actuators B144 can be motors, hydrauliccylinders, or other appropriate actuators and can be actuated by one ofa variety of methods, including all moving in synchrony, opposing pairsof actuators B144 or other functional groupings of actuators B144 movingin synchrony but not in synchrony with other functional groupings ofactuators B144, or all actuators B144 moving independently. Theactuators B144 perform both the retraction motion and the oscillationmotion. The actuators B144 can be wire or cable wound onto a spool thatis driven by a servo-motor or by a manually driven worm drive, with theblades B146 of the retraction elements attached to the wire or cable.Optionally, the retractor B140 can be instrumented with sensors thatmeasure the force on the blades B146 of the retraction elements, or thedisplacements of the blades B146 of the retraction elements, or anyother parameter relevant to the motion of the blades B146 of theretraction elements. The output from the sensors can be displayed byindicators B148 on the frame of the retractor B142 or on the monitor ofa computer attached to the retractor B140 via an electrical cable B150.

FIG. 24 shows another embodiment of a retractor B160 with multiple armsand actuators. Here there is a first actuator that generates theretraction motion by separating two halves B162, B164 of the retractorframe that resembles a Finochietto-style retractor. This first actuatoris a rack-and-pinion B166 driven by a hand crank, but, optionally, couldbe driven by a motor or other appropriate actuator. Additional actuatorsB168 attached to both halves B162, B164 of the retractor frame drive theoscillation motion of retractor blades B170. The additional actuatorsB168 can be driven by any appropriate actuator, such as a motor, a voicecoil, a piezoelectric driver, or a hydraulic actuator. The additionalactuators B168 can be rack-and-pinion in which the retractor blades B170are attached to the rack. The additional actuators B168 can be wire orcable wound onto a spool that is driven by a servo-motor with the cableattaching to the blade B170 of the retraction element. Alternatively,the actuators can be linear motors.

B.1.2 Angioplasty Balloons and Stents

Another common actuator for deforming anatomical tissues is the balloonused for angioplasty with or without placement of a stent. The deflatedballoon is inserted via a catheter into the blood vessel to be enlarged,and the balloon is inflated such that it presses against the walls ofthe blood vessel, enlarging the radius of that portion of the bloodvessel. Similar methods are used in valvuloplasty, where the diameter ofa heart valve is enlarged. Similar methods are used in tuboplasty toenlarge portions of the urinary tract and other surgical procedures toenlarge tubular anatomical elements, such as biliary tubes.

In the prior art, motions of the balloons are one-directional—they aresimply inflated with a sterile fluid. Sometimes several balloons ofincreasing diameter are used to enlarge the anatomical element inincrements, but each balloon is simply opened.

For angioplasty and valvuloplasty, inflation of the balloon is similarto the “retraction motion” described earlier for retractors. We presentinventions to impose an “oscillation motion”, as described above. Tosimplify the following discussion, each cycle of oscillation is dividedinto an “inflation phase” and a “deflation phase”.

In one embodiment depicted in FIG. 25, an angioplasty balloon B200 isinflated by a sterile fluid that passes through a catheter B202 from afirst syringe B204 that is used to generate the pressure to inflate theballoon B200. The retraction motion is inflation of the balloon B200,which is driven by the plunger B206 of the first syringe B204. Theseretraction motions are shown in solid black, single-headed arrows. Asecond syringe B210 is also connected to the catheter B202. A plungerB212 of the second syringe B210 oscillates in and out, cycling apressure that drives the oscillation motion of the balloon B200. Theoscillation motion of the balloon B200, and the associated oscillatingdrive of the plunger B212, are shown as asymmetric, double-headed arrowswith one arrow shape depicting the inflation phase and the other arrowshape depicting the deflation phase. Thus, oscillation of the pressureis achieved with a reciprocating motion of the plunger B212 such thatthe plunger B212 stroke length determines the amplitude of theoscillation and the plunger B212 stroke frequency determines thefrequency of the oscillation motion. Motion of fluid during thedeflation phase can be driven both by the combined elastic strain in thewall of the balloon B200 and in the wall of the anatomical element andby the rearward motion of the plunger B212.

In another embodiment depicted in FIG. 26, motion of fluid up thecatheter B202 for inflation of the balloon B200 is driven by a firstsyringe B204 as described for FIG. 25. The oscillation motion is drivenby a piston B224 that impinges on a drive membrane B222 separating fluidfrom the piston B224. This separation of fluid from the piston B224facilitates cleaning and sterilization of the moving parts formaintenance of sterility of the fluid. During the oscillation motion,the motion of fluid up the catheter B202 during the inflation phase isdriven by the piston B224. Motion of fluid in the opposite directionduring the deflation phase is driven by the combined elastic strain inthe wall of the balloon B200 and in the wall of the anatomical elementand by rearward motion of the piston B224.

One limitation of driving the inflation and deflation motions of thefluid up and down the lumen of the catheter is the resistance to fluidmotion imposed by the long, narrow catheter lumen. This high resistanceto fluid motion limits the frequencies and amplitudes attainable for theoscillation motion.

One means of eliminating the limitation is to restrict fluid motionduring both phases of the oscillation motion to short distances throughlarger diameter connections. This is achieved in the embodimentsdepicted in FIGS. 27 and 28. Consider FIG. 27, the balloon has twocompartments. A first larger diameter compartment B207 functions toforce the anatomical element B211 open (see FIG. 27C), and a secondsmaller diameter compartment B206 functions as a fluid reservoir. Secondcompartment B206 can be placed upstream, as depicted, or downstream fromthe first compartment B207. Fluid flows easily between the twocompartments through connecting channel B208. The retraction motion isdriven, as in the prior art, by pumping fluid up the catheter B212 toinflate the first compartment B207. The oscillation motion is generatedby forcing fluid back and forth from the second compartment B206 to thefirst compartment B207. The oscillation motion is thus driven by asecond actuator, comprising the second compartment B206.

One means for driving the motions of the second compartment B206 isshown in FIG. 28A. FIG. 28B shows an enlarged view of second compartmentB206. The second compartment B222 can be helically wound B226 with awire or cable made of a shape memory material, such as Nitinol.Electrical actuation of the Nitinol decreases the diameter, and thus thevolume, of the second compartment B222, forcing fluid through connectingchannel B208 into the first compartment B207 to drive the inflationphase of the oscillation motion. The deflation phase is then driven bythe combined elastic strain in the wall of first compartment B207 andthe wall of the anatomical element. The elastic strain driving thedeflation phase can also be augmented by a second helical wind (notshown) of spring material around the first balloon compartment B207.

In another embodiment depicted in FIG. 29, the angioplasty balloon B230has a single compartment B232 and is shaped as a cylinder, and theoscillation motion is generated in the walls of the compartment B232.FIG. 29A shows compartment B232 deflated, and FIG. 29B shows compartmentB232 inflated. Compartment B232 is inflated by flow B234 throughcatheter B212, driving the retraction motion. The two phases ofoscillation motion are driven by a first helical wind B236 ofshape-memory material, such as Nitinol, and a second helical wind B238of an elastic spring material. The first helical wind B236 ofshape-memory material causes the cylindrical compartment B232 todecrease diameter (and elongate to maintain constant volume), therebydriving the deflation phase. The second helical wind B238 of springmaterial stores elastic strain energy during the deflation phase thatthen drives the inflation phase when electrical actuation of the firsthelical wind B236 ends. Similarly, the two helical winds B236, B238 canbe wound such that electrical actuation of the first helical wind ofshape-memory material increases the diameter of the balloon driving theinflation phase, and elastic energy storage in the second helical windof material decreases the diameter of the balloon driving the deflationphase. Furthermore, shape memory material and elastic spring materialcan be included in the first helical wind B236 and in the second helicalwind B238 such that actuation of one helical wind B236, B238 and thenthe other helical wind B236, B238 drives both phases of oscillation.Furthermore, only shape memory material can be included in the firsthelical wind B236 and in the second helical wind B238 such thatactuation of one helical wind B236, B238 and then the other helical windB236, B238 drives both phases of oscillation.

In another embodiment depicted in FIG. 30A, the angioplasty balloon B250has a single compartment B252 and the oscillation motion is driven by abubble generated inside the compartment B252. The retraction motion isdriven by inflation of the compartment B252 by fluid motion up the lumenof the catheter B212. The oscillation motion is driven by a smallelectrical heater B254 mounted onto a wire B256 inside catheter B212underlying the compartment B252 such that a bubble B258 of water vaporis formed, driving the inflation phase of the oscillation motion. Heatdissipation to the surrounding fluid and tissue causes the vapor bubbleB258 to collapse, driving the deflation phase of the oscillation motion.Similarly, electrolytic bubble generation of a bubble B258 inside thecompartment B252 could drive the oscillation motion.

In another embodiment depicted in FIG. 30B, high frequency ofoscillation is generated by a piezoelement. Angioplasty balloon B270 hasa single compartment B272 and the oscillation motion is driven by apiezo-vibrator B274 mounted on a wire B276 inside the compartment 13272.The retraction motion is driven by inflation of the compartment B272 byfluid motion up the lumen of the catheter B212. The oscillation motionis driven by actuation of piezo-vibrator B274 which emits high-frequencypressure waves B280 which transmit as high-frequency, low-amplitudeoscillations of the wall of compartment B272.

B.2 Measurement of Tissue Properties

Oscillating deformation of a tissue with simultaneous measurement ofselected parameters (e.g., force, displacement) can yield importantinformation about the tissue's material properties and physiologicalstate.

Leveque et al. (Leveque, Rasseneur et al. 1981) disclose oscillatingloading for measurement of the Young's modulus and the internal dampingfactor of a viscoelastic material, including excised biological tissues,by oscillating loading. Long et al. (Long 1992; Long, Pabst et al. 1997)disclose measurement of the dynamic bending stiffness and dampingcoefficients of isolated intervertebral joints that are loaded byoscillating bending.

There are two disclosures for measuring the mechanical properties of anintact biological tissue:

-   -   1. Brown and Holmes (Brown and Holmes 1990) disclose a method        for measuring the mechanical properties of intact tissues, and        they disclose only constant velocity deformation as a means for        standardizing measurements for spinal instability; and    -   2. Huszar (Huszar 1984) discloses a modified version of the        technique of Leveque et al. (Leveque, Rasseneur et al. 1981) to        make a measuring device that applies a force on the uterine        cervix to measure the modulus of extensibility of the tissue in        situ; the purpose is to assess the status of the cervix during        obstetric procedures, especially for pregnancy, and Huszar also        suggests use for ear or skin.

Measurements on intact tissues, as opposed to excised tissues, limitsdirect applicability of the above techniques disclosed for measuringmechanical properties by oscillating loading. This is due to the unknowndimensions of the intact tissues, unknown mass and connectivity tosurrounding tissues, etc. However, modifications we disclose permit thecollection of information relevant to the mechanics and physiology ofthe tissue being retracted or dilated. Importantly, these modificationscan provide information relevant to the processes of retraction ordilation.

In one embodiment, as disclosed in Section B.1.1.1 and shown in FIG. 12,simultaneous measurement of force and displacement during oscillatingloading permit measurement of effective stiffness (the slope offorce/distance of displacement) and of viscous losses (area bound byhysteresis of the force/displacement curve seen during one cycle ofloading/unloading). Furthermore, accelerated force relaxation AFR can bemeasured as disclosed in Section B.1.1.1.2 and shown in FIG. 31 todetermine when to end an oscillation period. As shown in FIG. 31, a timeconstant t for accelerated force relaxation AFR can be determined byfitting a decay curve to the minimum force points for each oscillation,and cyclic loading can then be terminated when a fraction of the timeconstant has expired. For example, when retracting a tissue, thefollowing sequence of steps can be followed:

-   -   (1) a retraction motion B300 is performed;    -   (2) retraction is paused;    -   (3) an oscillation motion B302 is performed with measurement of        force and real-time calculation of the time constant τ, B304 of        the force relaxation as shown in FIG. 31; such that when a time        equal to the time constant τ, B304 has elapsed;    -   (4) oscillation motion B302 ceases; and    -   (5) retraction motion B300 resumes.        This algorithm can be used to optimize the reduction of force        during a retraction (maximum force decrease in the smallest        amount of time). Similarly, the oscillation can be stopped when        some fraction or multiple of the time constant is achieved.        Conversely, the force decrease can be monitored, and the        oscillation motion terminated when the force has declined by a        specified amount or percentage of the starting force.

In another embodiment shown in FIG. 32, decline in effective stiffnessof a tissue can be measured arising from oscillating loading viaphenomena such as work softening. Effective stiffness(force/displacement, dF/dx where F is force and x is distance) decreasesin a tissue that displays work softening. Measurement of force anddistance during repeated cycles of loading/unloading permit comparisonof stiffness during each successive loading (or unloading). Thus, asshown in FIG. 32, which shows two (2) cycles of loading, the forcedisplacement trace begins at B310 and ends at B312. As an example, theeffective stiffness of the material during the first cycle of loading isestimated as the slope of the line B314, drawn between the limits ofminimum and maximum displacement for that cycle, and, again, during thesecond cycle as the slope of the line B316. The decrease in slope fromline B314 to line B316 is then used as an estimate of the degree of worksoftening. Comparisons of effective stiffness can be made repeatedly, inreal time, during oscillating loading. The embodiment of a retractordescribed in Section B.1.1.1 would serve for such measurements. Anotherembodiment would be an angioplasty balloon in which pressure and volumein the balloon are measured during oscillating loading, such that volumeis used as an estimate of displacement and pressure is used as anestimate of force. Pressure can be measured with any appropriatepressure gauge. If loading is at a low frequency, then measurementanywhere in the fluidic system would suffice because pressure gradientsthat drive flow into the balloon would be small. If loading is at higherfrequencies, the measurements can be made inside the balloon withseveral methods including miniaturized pressure sensors (membranedeflection, capacitance based, etc.) Volume can be measured by measuringthe displacement of fluid in the balloon by means such as pistondisplacement, or with a mass flow sensor placed along the channel to theballoon. The diameter of the balloon can also be used to directlydetermine deformation of the anatomical part or to estimate the volumeof the balloon. The diameter of the balloon can be measured acousticallyor optically via reflection of radiation off the wall of the balloon.

Viscous losses during deformation of the tissue can be estimated by anyof several methods, including: measuring the phase lag between force anddisplacement, measuring the area bound by the hysteresis curve duringone cycle of loading/unloading, or measuring the difference in workperformed by the motor during loading and unloading.

The resonant frequency of the materials may be measured by oscillatingat different frequencies as disclosed by Leveque et al. (Leveque,Rasseneur et al. 1981), by identifying the frequency at which the forcerequired for deformation is smallest, by identifying the frequency atwhich viscous loss is smallest, or by other methods known in the fieldsof mechanics and biomechanics.

Many methods of testing by oscillation require testing at multiplefrequencies of oscillation. This can be accomplished by testing atmultiple discrete frequencies, testing via a frequency sweep, or testingwith “white noise”.

B.3 Tissue Deformation Via Oscillating Loading, Tissue Measurement, andFeedback

Information obtained by measurements such as those disclosed in SectionB.2 can be used to make decisions about how best to perform a tissuedeformation by either oscillating loading (e.g., an oscillation motion)or normal one-directional loading (e.g., a retraction motion).

In one embodiment, force and displacement are measured by a retractor.Alternating retraction motion and oscillation motion are used. Aretractor similar to that in Section B.1.1.1.1 and shown if FIG. 12 canbe used. The first phase of retraction proceeds as follows:

-   -   (1) The retraction motion starts, during which the distance is        measured, and the retraction motion is stopped when a fraction        of the desired opening is reached, e.g. 10% or 30%;    -   (2) Oscillation motion is then imposed to determine the        frequency that results in the smallest time constant τ for        accelerated force relaxation (AFR).    -   (3) Oscillation motion is then continued for a duration of 1.5τ        and then stopped; and    -   (4) Retraction motion is resumed.        This cycle is repeated, possibly with different opening extents        (e.g. another 10% of desired opening or another 20% of desired        opening) until the desired opening is obtained.

In another embodiment, the stiffness of the material is used todetermine when an oscillation motion begins. Force (F) and distance (x)are measured by the retractor, and stiffness is measured in real-time asdF/dx. Alternating retraction motion and oscillation motion are used asdescribed in the preceding paragraph. Retraction proceeds as follows:

-   -   (1) Retraction begins with a retraction motion, and stiffness is        measured throughout motion. When stiffness starts to decrease,        indicating the material properties of the tissue are changing,        retraction motion stops;    -   (2) Oscillation motion commences with an amplitude of        approximately 2 mm and a frequency of approximately 5 to 10 Hz,        or with an amplitude of approximately 4 to 8 mm and a frequency        of approximately 0.5 to 2 Hz;    -   (3) Oscillation occurs for approximately 10 to 50 cycles to        alter the material properties of the tissue such that stresses        in the tissue are relieved and large-scale tissue components        don't break; and    -   (4) retraction motion is resumed.        Other frequencies and amplitudes can be used, and frequency and        amplitude can be adjusted for the tissue to be retracted, with        bone, for example, being oscillated at a frequency of kHz and an        amplitude of micrometers. The oscillation motion can be any        combination of frequency and amplitude that achieves appropriate        modification of the tissue being retracted.

In another embodiment, retraction and oscillation motions aresuperimposed. Retraction follows a pre-determined trajectory (e.g., atrajectory in which the retractor blades move apart quickly at first butincreasingly slowly as retraction proceeds such that the desired openingis achieved in a proscribed time, such as that shown in FIG. 11B). Forceand distance are measured. Oscillation serves both to accelerate forcerelaxation, which now occurs concomitantly with continuous deformation,and to permit repeated stiffness measurements, as shown in FIG. 32) toregulate the velocity of the retraction motion about the predefinedtrajectory (e.g., if stiffness is too high, then the velocity of theretraction motion slows, or if the stiffness is too low, then theretraction motion accelerates).

In another embodiment, pressure in the tissue is measured by a cathetersensor, such as the miniaturized sensors from Scisense, Inc. of London,ON, Canada and ADInstruments of Colorado Springs, Colo., USA. One ormore pressure sensors are placed into the tissue near the retractorblades, such that the pressure sensors sense internal tissue pressureand how internal tissue pressure rises during retraction. Alternatingretraction and oscillation motions are used. Retraction motion startsand proceeds until tissue pressure reaches a threshold (e.g., a levelthat indicates that perfusion of the tissue has stopped). Retractionmotion is halted and oscillation motion is started. Oscillation motionis used for accelerated force relaxation until the pressure drops belowthe threshold. Retraction motion is resumed, and the process repeateduntil the desired opening is achieved.

C. Detecting Tissue Trauma During Retraction

FIG. 33 presents an example of a Finochietto-style retractor C4 in theprior art. The retractor C4 has a fixed retraction element C6 attachedto one end of a rack C8 of a rack-and-pinion drive C10 driven by amanual drive handle C12. A moveable retraction element C14 is attachedto the rack-and-pinion drive C10 and moves along the rack C8. Each ofthe retraction elements C6, C14 has a single blade C16 that engages thetissue to be retracted.

A retractor C4, such as that shown in FIG. 33, can be instrumented tomeasure several parameters during retraction. For example, the bladesC16 of the retractor C4 can be fitted with force sensors (such as straingauges or a load cell), and the separation of the blades C16 can bemeasured by fitting a displacement sensor onto the retraction elementsC6, C14 (such as a linear potentiometer or an optical encoder). Theoutput from these sensors can be fed into a display (such as a digitalnumeric display or a bank of light emitting diodes LEDs) for directreadout, or the signal can be fed into an analog-to-digital converterand read by a computer for subsequent calculations and display. Multiplesensors measuring a parameter (for example, a plurality of load cellsand/or accelerometers indicating forces and/or accelerations acting on acorresponding plurality of retractor blades) can provide a map in twodimensions (2D), three dimensions (3D), or four dimensions (4D, withtime) of the forces and moments acting on the system consisting of thebody of the patient and the retractor C4.

FIG. 34 depicts the retractor C4 showing how it might be fitted with aset of calipers C22 for measuring the separation of the retractionelements C6, C14. Additionally, strain gauges C20 can be placed on eachof the two blades C16 of the retraction elements C6, C14 (“retractorblades”) to measure forces on the retractor blades C16.

FIG. 35 shows a retractor C28 that uses a bi-directional ball screw C30(i.e., having two followers that travel in opposite directions) that isdriven by a stepper motor C32 which in this case is a MDrive 23Plus fromIntelligent Motion Systems, Inc. The bi-directional ball screw C30 ismounted to a rail C34 with two linear translation stages C36 which inthis case is the IKO LWHG 25 from IKO, Inc. such that each translationstage C36 attaches to one of the bearings on bi-directional ball screwC30, thus when bi-directional ball screw C30 is rotated by the steppermotor C32, the translation stages C36 travel in opposite directions. Aretractor arm C38 fabricated by hand from mild steel angle iron that wascut/bent/welded into shape, is mounted to each translation stage C36.Each retractor arm C38 has a retractor blade C40 fabricated by hand withmild steel.

A linear potentiometer C42 which in this case is a 5 kOhm, 100 mm linearpotentiometer from Schaevitz is used to measure separation of theretractor blades C40. The static mount of the potentiometer C42 isaffixed to the rail C34, and the piston of the potentiometer C42 isaffixed to one of the translation stages C36. Note that any means ofmeasuring displacement could be used here, such as optical encoders,contact and non-contact proximity sensors, digital calipers, and thelike.

The retractor blades C40 are instrumented with a full-bridge straingauge assembly (not shown) which includes two (2) gauges, which in thiscase are model CEA-06-125UN-350 from Vishay Micro-Measurements, Inc., oneach side of the blade. The signal from the strain gauges is theamplified by a signal conditioner (not shown) which in this case wasmodel OM-2 from 1-800-LoadCells. Note that force could be measured byany of several means, such as drive current on the motor (and othermeans of measuring torque on the drive mechanism), fiber optic straingauges, optical sensors of deformation, and the like.

All signals from the linear potentiometer C42 and the signalconditioners/strain gauges are read by a Windows-based computer using adata acquisition card, which in this case is a model USB-6211 fromNational Instruments, and software, which in this case is LabVIEW fromNational Instruments, Inc. using a custom program prepared by KatyaPrince of Prince Consulting. The stepper motor C32 is controlled withIMS Terminal software from Intelligent Motion Systems, Inc. Note that aservo-motor could also be used. The strain gauges were calibrated byhanging known weights from the retractor blades C40 of the retractorC28. The linear potentiometer C42 was calibrated with a metric ruler.

A series of experiments were conducted with the prototype retractor C28described above using parts from pig cadavers. The parts were a “frontquarter” purchased from Nahunta Pork Center (Pikeville, NC). A frontquarter is basically a whole pig cut at the waist (forming a front half)and split down the vertebrae (forming left and right quarters); thus,each quarter had an intact rib cage (one side), spine (bisected),sternum (bisected), and shoulder. All parts had been refrigerated afterslaughter, used within 24 hours of slaughter, and warmed by immersion inwarm water (while wrapped in a plastic bag to prevent soaking of thetissue) to near body temperature (31° C. to 37° C.). The quarters rangedin size from 8 to 12 kg.

We performed thoracotomies between 3-4 rib pairs on each quarter, almostalways performing an incision between ribs 5-6, 7-8, 9-10, and 11-12.Thoracotomies were performed by:

-   -   cutting the skin with a scalpel over the range of the        thoracotomy, and in a direction parallel to the ribs,    -   bisecting the muscles overlying the ribs with a scalpel,    -   cutting through the intercostal tissues with a scalpel,    -   pushing a finger between the ribs to make a small opening,    -   inserting the closed blades of the retractor into the opening,    -   positioning the retractor such that the blades sat approximately        halfway between the spine and the sternum and the retractor's        axis of opening was approximately parallel with the spine,    -   initiating opening according to a specified algorithm via        computer control of the stepper motor.

Incisions were typically 110 mm to 130 mm long, with longer incisionsbeing performed on larger quarters.

FIG. 36 shows data from the retractor C38, with force C50 anddisplacement C52 (distance measured by the linear potentiometer C42)plotted with respect to time for a “standard retraction”, similar tothat defined by Bolotin et al. (US Patent Application Publication Number2006/0025656 and 2007, J. Thorac. Cardiovasc. Surg. 133:949), whichproceeds as follows:

-   -   open to 40 mm in one (1) minute (⅔ of final opening);    -   pause two (2) minutes for force relaxation; and    -   open to 60 mm in three (3) minutes (i.e., to the final opening).

Thus, a total opening of 60 mm is reached in 6 minutes. Each of the twomoves is constant velocity (40 mm/min for the first and 6.8 mm/min forthe second). These moves were controlled by a computer program executedin a computer with the IMS Terminal software. Thus, unlike Buckner andBolotin et al. (US Patent Application Publication Number 2006/0025656and 2007, J. Thorac. Cardiovasc. Surg. 133:949) the velocity of theretraction motions was precisely controlled. This somewhat matches thepace described to us by other thoracic surgeons, but there is nostandard clinical practice. Surgeons use a procedure defined by theirtraining, personal experience, patient condition, and sense-of-touch(i.e., non-quantitative) estimates of force applied at the handle of ahand-cranked retractor. Furthermore, surgeons have no velocity control,other than hand-eye coordination. Importantly, the self-lockingFinochietto-style rack-and-pinion drive C10 engages and advances inrather abrupt half-step turns of the handle C10, producing a non-linearrelationship between rotation and motion of the retractor blades C16,making control of velocity and force difficult.

FIG. 37 shows the displacement and force on both arms for a Finochiettoretractor instrumented like the retractor shown in FIG. 34, except thata linear potentiometer is used to measure displacement, instead of thecaliper shown in FIG. 34. These measurements are from a thoracotomyperformed on an anesthetized pig (female, 50 kg weight, proceduressimilar to those in FIG. 36 except that opening was to 52 mm in oneminute without a long pause in retraction). The force and displacementtraces in FIG. 37 are not smooth. Both traces show the step-by-stepincreases generated by the ½-rotations of the crank. Furthermore, evensmall adjustments or other motions of the crank resulted in largedeflections in the force trace. For example, when the surgeon simplyadjusted the position of his hand on the crank at 42 s, an approximately30 N change in force is seen in the force trace for both retractorblades. During this retraction, a rib broke. Importantly, the point onthe trace where the rib broke could not be identified in any of thetraces. The point C56 on the trace where the rib broke was identified bycareful analysis of a time-correlated video recording of the procedurein which the break could be heard as a “crack”. Thus, it is not possiblefrom these force or displacement traces to detect that a rib is about tobreak. Nor is it possible to determine if a rib breaks.

Returning to FIG. 36, the force of the motorized retraction risesrapidly over the first minute of retraction (opening to 40 mm). Forcerelaxation, as described in Buckner and Bolotin et al. (US2006/0025656and 2007, J. Thorac. Cardiovasc. Surg. 133:949), and also illustrated inFIG. 1, is evident during the two-minute pause—the force required tomaintain the 40 mm opening decreases with time. Force again rises whenretraction is resumed at 3 minutes, rising at a time-varying rate, butthe increase in force is smooth up until 60 mm retraction is achieved.

No significant tissue breaks occurred during the retraction shown inFIG. 36. Two small breaks are evident over the first 50-60 s interval,as evidenced by small downward deflections in the force trace (marked byarrows). The absence of significant breaks is unusual. Most retractionsof this type resulted in large tissue breaks, as seen in FIGS. 38A-38Cand 40A-40B (discussed below).

FIG. 38A shows data from another retraction, using the same motorizedstandard retraction as in FIG. 36. A large break is seen—a break thatspanned several seconds (46-70 s on the graph, marked with an asterisk)and ended only with the start of the pause period. There are alsoseveral smaller breaks (marked with arrows), also evident as significantdrops in the slope of the force plot. FIG. 38B shows an expanded view ofthe data from 20 to 70 s, showing the large break. There are two typesof events that precede this large break. The first type of event is adecrease in the slope of the curve beginning at 38 s (illustrated by thetwo dashed lines—termed a “slope event”). The second type of event is asmall break seen as a drop C60 in force at 42 s, marked with an arrow inFIG. 38B (termed a “force event”). Note that there is a second forceevent C62 at 44 s. FIG. 38C shows the interval from 41.5 to 45 secondson an expanded scale; the two force events, the first force event C60 at42 s and the second force event C62 at 44 s, are clearly visible.

The two types of events, slope events and force events, preceding thelarge break are better seen in FIG. 39 which plots both the force (kg)and the slope of the force (kg/s) for the interval of 10 to 46 s in theretraction shown in FIG. 38. A slope event C70 beginning at 38 s is morevisible, and the two small breaks are now much more prominent asnegative-going peaks marking the first force event C60 and the secondforce event C62.

FIGS. 40A and 40B present another example of a standard retraction—FIG.40A presents data from the entire retraction, and FIG. 40B presents amagnified view of one minute of data from 30 s to 90 s. In thisretraction, there is, again, a large break C100 at the end of the first1-minute of retraction, beginning at about 72 s. Several small forceevents occur (e.g., at 57 s, 59 s, 61 s and others), but preceding theseis a slope event C102 beginning at 57 s. This drop in slope C102 is moreobvious than the slope event C70 seen in the retraction shown in FIGS.38 and 39. The slope event C102 in FIG. 40 is evident in the forcetrace, but is more easily seen in the slope trace. Another commonfeature is evident here—both the force trace and the slope trace becomenoisier; their variance increases. This provides third and fourthindicators of an imminent break—termed a “force variance event” and a“slope variance event”.

All four of these events, (a) a force event, (b) a slope event, (c) aforce variance event, and (d) a slope variance event are frequently seenpreceding a large break and can be used as indicators that a large breakis about to occur.

Note that higher order time derivatives of the force trace (e.g.,d2F/dt2, etc) also present information relevant to imminent breaks andcan make a distinction from baseline simpler because the signal staysnear zero. FIGS. 41A and 41B show the second time derivative, d²F/dt²,of the force for the retractions presented in FIGS. 38, 39, and 40.(FIG. 41Aa presents the retraction from FIGS. 38 and 39, and FIG. 41Bpresents the retraction from FIG. 40.) In FIG. 41A, the force event C60at 42 s and the force event C62 at 44 s are now clearly resolved asnegative-going spikes C200 and C202. In FIG. 41B, the slope event at 57s is now clearly resolved as a large, negative-going spike C210. Thus,the second time derivative of the force provides both (a) a flatbaseline over much of the retraction and (b) a negative-going spike atforce and slope events providing a clear signal indicating the onset ofthe variance. Detection of the spike can be accomplished by comparisonof substantially instantaneous values of d2F/dt2 versus a time-averagedvalue of d2F/dt2, with the ratio of instantaneous/time-averaged valuesof d2F/dt2 exceeding a predefined threshold, or by comparison ofinstantaneous values of d2F/dt2 with variance of d2F/dt2 measured over apreceding time interval, such as the ratio of the instantaneous value ofd2F/dt2 with the sum of squares of d2F/dt2 over the preceding 20 s orover the preceding 4 s. There are many such detection algorithmswell-established in the art of signal processing that can be used todetect a negative-going spike in d2F/dt2.

Implementation of these indicators within automated control systems inmedical devices would permit both (a) the presentation of indicators tothe physician, permitting the physician to take corrective action beforea break occurs, and (b) automated operation whereby the device containsappropriate mechanisms to implement corrective action. Software executedby microprocessors can perform appropriate signal processing (e.g.,Butterworth filter, Fourier analysis, etc.) of signals from sensors toimprove signal-to-noise, and this software can also perform automaticevent detection with automatic response. For example, an automatedsystem can initiate a pause in the first phase of retraction if anegative-going spike in d²F/dt² is detected, or an automated system caninitiate an oscillating motion in the first phase of retraction if anegative-going spike in d2F/dt2 is detected.

Importantly, detection of these events requires a stable force-timetrace. This requires a means of regulating the velocity of retraction toensure that it maintains a commanded velocity free of substantialvariations in velocity; for example, the retraction velocity remainsconstant during measurement, or the trajectory of motion during thefirst phase of retraction follows a substantially parabolic profile,retracting more quickly at first and increasingly slower as retractionapproaches a desired opening of the surgical incision or a desireddilation of the artery. This can be accomplished with a retractionsystem with manual actuation permitting very smooth motion, such as ahydraulic actuator or a fine pitched lead screw. Preferably, retractionis performed by a motor-driven retractor such that velocity can bemaintained at predetermined rates by internal control, such as by anopen-loop system with a stepper motor that is capable of generatingsufficient torque as to not be impeded by retraction forces or by aclosed-loop system with a servo-motor. Closed loop control of velocityin a hydraulically-actuated system is also possible. The velocity ofretraction can be constant, but this is not necessary. For example, asmoothly time-varying velocity can be used.

FIG. 42 depicts an example of an algorithm C300 for detecting imminenttissue trauma. The algorithm C300 can be used for any retraction profile(displacement over time) with any device that measures force. Thealgorithm C300 searches for both a negative-going spike in the forcetrace and for an increased variability (“noisier”) force trace. The userinputs two thresholds, T_(S) for detecting the negative-going spike andT_(V) for detecting increased variance. The thresholds T_(S) and T_(V)allow the user to set the sensitivity of the algorithm C300. Forexample, a surgeon might choose to use a more sensitive setting for apatient expected to have fragile bones. Variability in the force signalis calculated as the root-mean-square (RMS) of the force trace, as shownin FIG. 42. Execution of the algorithm C300 starts (block 0302) at theinitiation of retraction. Retraction proceeds for N+0.1 seconds (blockC304), with force sampled at a rate equal to or greater than 10 Hz. Thealgorithm C300 then calculates RMS of d²F/dt² over the last N seconds(block C306), skipping the first 0.1 second to avoid transients from thestart of retraction (e.g., motor stiction, etc.). The algorithm C300first looks for a negative going spike in d²F/dt² by comparing the lastmeasurement to the RMS over the last N seconds (RMS_(N)) multiplied bythe threshold T_(S) input by the user (d²F/dt²<(0−TS*RMS_(N))) (block308). If the force is more negative than this parameter, then a 20 spause in retraction (block C310) is triggered permitting forcerelaxation in the tissues, and the algorithm C300 returns to the start(block C302). If d²F/dt² is not more negative than this parameter, thenthe algorithm C300 checks for increased variability in d²F/dt² bycomparing the RMS over the past 0.5 seconds (RMS_(0.5)) to the RMS overthe past N seconds (RMS_(N)) multiplied by the threshold T_(V) (blockC312). If RMS_(0.5) is greater then a 20 second pause (block C310) inretraction is triggered permitting force relaxation in the tissues, andthe algorithm C300 returns to the start (block C302). If RMS_(0.5) isnot greater then retraction proceeds for another 0.1 second (block 0314)and checks again (block 306). Thus, force is checked for anegative-going spike in d²F/dt² and for increased variability in d²F/dt²every 0.1 seconds. The force trace can be checked more or lessfrequently. Other sampling frequencies can be used. The 0.1 second addedto N in block C304 can be any other time interval sufficient to avoidtransients in the force trace on starting the motor or around any otherevent deemed spurious to detecting tissue trauma. The event triggered bythe detection algorithm (a 20 second pause in this case) can be anyevent that is appropriate to the detected signal. For example,retraction can pause with continued measurement of force and thenretraction can resume after the slope of the force trace becomesshallow, indicating that force relaxation has approached a limit.Another example is to initiate an oscillation of the retractor toaccelerate force relaxation, or to pause for a first period and then tooscillate for a second period.

There is a fifth event for predicting imminent large breaks in tissueduring retraction. Breaks are audible. Snaps and pops (“audible events”)are heard throughout a retraction. Big breaks are louder. The largebreak at 46-70 s in FIG. 38B was actually a series of repeated fracturesof the tissue. This was audible as a rapid series of loud audibleevents. Thus, the audible events of tissues breaking can be used as anindicator of tissue trauma, and audible events, including less loudevents, can be used as indicators that a larger traumatic event is aboutto occur. Also, the qualities of an acoustic signal (e.g., the frequencyof occurrence of audible events) can be used as an indicator ofimpending trauma. In the preceding example, the frequency of occurrenceof acoustic events becomes higher as trauma increases.

FIG. 43 depicts how such a trace would look—two breaks occur, one atabout 55 s and another at about 255 s (marked with an asterisk). Theseare preceded by audible events (marked by arrows). These audible eventsmight be distinguished from background noise by sound intensity,spectral composition, or both. In another example, the acousticfrequency (i.e., the pitch) of each acoustic event might change; forexample, the pitch of earlier events might be higher than the pitch oflater events as the tissue approaches a large fracture.

Sound measurement can be performed by microphones or other sound sensorsplaced in the air near the incision; on the retraction device, such aswith a contact microphone; or on the patient's body, for example, with acontact microphone embedded in a gel beneath an adhesive pad, in whichthe gel matches the acoustic conduction of the body. If the soundmeasuring device is placed on the patient's body, then multiple soundmeasuring devices placed at distinct locations can be used to detect theposition of the fracture either by relative intensity of the sound or bydetecting time-of-arrival for triangulation of the location of thefracture or the propagation of a locus of damage.

Acceleration can serve as a sixth event indicator. When a large ligamentsnaps during retraction, the entire retractor suddenly shakes, as willall or a portion the body of that patient (depending on the magnitude ofthe tissue trauma event). With a smooth retraction, even smaller soundscan be “felt” with fingertips that lightly touch the retractor.Accelerometers are ideally suited to measure these motions.Accelerometers mounted on elements such as the body of the retractor, onthe retractor blades, and/or on the body of the patient would provide anindication of the motions of any, some, or all of these elements.Acceleration is thus indicative of any number of a range of eventsoccurring within (or to) a patient's tissues, including incipient tissuetrauma. In this way, acceleration can serve prognostic goals.Acceleration can also provide feedback, to track the behavior of thedevice itself.

An accelerometer typically measures acceleration along a single axis.Accelerations acting directly along this axis produce the strongestsignal, while accelerations acting exactly perpendicularly to that axismay produce little or no signal at all. In an actual patient's body,with complex tissues and force transmission paths, one may encounter thesituation where one cannot expect an accelerometer associated with thatbody to ever register a zero output. One might mount one or moreaccelerometers to a surgical instrument (for example, the body of aretractor), to a portion of a surgical instrument (for example, one, twoor a plurality of a retractor's blades), and/or to a patient's body.With its axis oriented at a carefully chosen angle with respect to thelocal axis of retraction, a given accelerometer can provide indicationsof not only an early warning of impending tissue trauma, but also alocal direction of interest with respect to those accelerations, and acomplex time series of accelerations associated with specific tissuetypes or tissue behaviors. As with the acoustic event detection above,one can use accelerometers to detect (a) acceleration events, (b)acceleration slope events, (c) acceleration variance events, and (d)acceleration slope variance events.

Attaching multiple accelerometers at multiple locations and/or anglescan provide a picture, or map, in 2D, 3D, or 4D (with time) of theforces and moments acting on the system consisting of the body of thepatient and the retractor. This picture can enable a surgeon (or thecorrective software) to know which tissue type (or which of many tissueelements) might be involved, and/or when and where tissue trauma willoccur before the onset of major damage. As one example, accelerationsparallel to the surface of a given retractor blade might indicate theincipient failure of fibrous connective tissue (e.g., fascia orperiosteum) oriented in that direction, while accelerationsperpendicular to the surface of that retractor blade might indicate theincipient failure of the rib that that retractor blade is moving. As forcorrective actions, in that example one might try to prevent snappingconnective tissue by initiating oscillating loading, whereas one mightinstead respond to prevent rib breakage by pausing the retraction.

Furthermore, accelerometers might also provide independent confirmationof how well the actual behavior of a motorized instrument (such as aretractor) is conforming to the commanded behavior (whether controlledby the surgeon, the software, or some combination of the two). Thiscould serve as an on-the-fly diagnostic to permit active self-correctionand self-calibration. Accommodation and re-modulation can correctperformance variances should they occur, further increasing confidencein the safe operation of the device.

A further aspect of self-operational feedback features (e.g., foracceleration) is that the device could adapt to the different operatingstyles of surgeons, for example by enabling detection of the operator'sinstrument handling patterns. For example, an accelerometer mounted tothe retractor can be used to detect motions of the retractor arisingwhen a surgeon inadvertently touches the retractor (e.g., wheninspecting the incision) or purposefully handles the retractor (e.g., toadjust the position of the retractor). Such inadvertent touches orpurposeful handling of the retractor can create transients in thesignals that resemble imminent trauma. Signals from the accelerometercan be used to discriminate transients in the force and/or sound tracesarising from the surgeon's actions.

Using any of these events for detecting an imminent tissue fracture orother damage, it is possible for a surgeon or an automated system totake corrective steps to prevent the tissue fracture. For example, upondetection of an event, retraction can be paused, permitting forcerelaxation, or retraction can switch from constant velocity retractionto an oscillating loading to use work softening of the tissue (orrelated phenomena arising from oscillating loading) to either induce anaccelerated force relaxation or to create many small tissue fracturesthat relieve the stress in the tissue and prevent fracture of a majortissue component.

It is important to recognize that the techniques described here fordetecting imminent tissue trauma by measuring force and sound, coupledwith detection of transients, can be used without prior knowledge of aparticular patient's physiology or pathology—the signals are unique totissue trauma, but independent of a patient's unique characteristics.Thus, tissue trauma can be detected whether a patient is old or young,large or small, osteoporotic or normal. There is no requirement fordetermination of a threshold force to try to avoid tissue trauma, nor isthere any need for databases of patients' characteristics and relatedforce-distance measurements for adjusting retraction to unique patientparameters.

There are any number of other tissue trauma early warning eventindicators. The aforementioned examples are only intended to teach theprinciple of early detection, not limit the embodiments of sensingmodality to force, sound, and acceleration.

F. Self-Balancing Retractor Blades

FIG. 44 presents an example of a Finochietto-style retractor F2 in theprior art. It has a fixed retraction element F6 attached to rack of arack-and-pinion drive F10 that is manually driven by rotation of thedrive handle F12. A moveable retraction element F8 is attached to thedrive of the rack-and-pinion drive F10. Each of the retraction elementsF6, F8 has a single retractor blade F4 that engages the tissue to beretracted.

The forces under the retractor blades F4 can be large. Furthermore, anedge of a retractor blade F4 can become a point-load if the retractorblade F4 is not well-seated or if the retractor blade F4 contacts acurved surface, such as a rib. If a retractor blade F4 becomes a pointload, then the stress in the tissue at the point of loading can becomeextreme. Broken ribs are common using these types of devices.

Such maladjustments of a blade can be reduced if several blades are usedto engage the edge of an incision. FIG. 45 shows a retractor 300 in theprior art from the lab of Greg Buckner (Buckner and Bolotin 2006;Bolotin, Buckner et al. 2007). This retractor has six retractor blades200 attached to a common frame 700. Each retractor blade 200 has anintermediate member 220 that connects the retractor blade 200 to anactuator 300. Thus, each retractor blade 200 has its own actuator 300.FIG. 45A is a diagram of the retractor 300. FIG. 45B is a photograph ofthe retractor 300 being used in a thoracotomy in a sheep, demonstratinghow the retractor blades 200 engage the margins of the incision. The useof multiple retractor blades 200 along the margin of the incisiondistributes the retraction forces, reducing the force on any singleretractor blade 200. However, the load on any single retractor blade 200is determined by how hard it pulls on the incision as set by theactuator 300 of that particular retractor blade 200. Adjusting theforces to be equivalent to one another, or to have any other desireddistribution of forces, requires individual adjustment of all theactuators 300 which must be made by an operator (which would be slow andirregular) or by an automated system combining force measurement,motorized actuators, and a control system (which might be expensive).

Discussion of the next section requires review of a piece of very oldprior art, related to the harnesses of draught horses that pull wagons.A “swingletree” is a pivoted, suspended crossbar to which the two tracesof a horse's harness are attached when it pulls a wagon. FIG. 46 shows atop view of a swingletree F94 attached to wagon F97 by first harnesscomponent F104. Swingletree F94 attaches to harness component F104 atpivot F98. Two traces F96 of the harness extend from swingletree F94 tothe collar F92 against which horse F90 pulls, exerting force F106 met byreaction force F107 and creating force F108 on the pivot F98 and forceF102 on the wagon F97. If due to uneven motion of the horse, the forceon traces F96 become unbalanced, then the moment about pivot F98 causesswingletree F94 to rotate until the forces on the traces F96 becomebalanced.

Every horse F90 attached to a wagon F97 pulls against a swingletree F94.When more than one horse pulls a wagon, multiple swingletrees aretiered, as shown in FIG. 47. Two horses F110 and F112 pull a wagon F124.Each horse F110 and F112 pulls on its own (child) swingletree F120, andthe two swingletrees F120 are attached to a third (parent) swingletreeF122 that is also known as a “doubletree”. The entire structureconnecting the swingletrees F120 and F122 is a tensile one, and rotationof swingletrees F120 and F122 balances the forces on each swingletree.Ultimately, the pivot F130 ensures that only a tensile force is appliedto wagon F124, and rotation of the swingletrees F120 and F122 isolatesall unbalanced forces from wagon F124.

FIGS. 48A and 48B show another retractor F150 in the prior art. This isthe Skyhook from Rultract (www.rultract.net, U.S. Pat. No. 4,622,955).The retractor F150 is a hoist, suspended above a patient F163, with tworetraction rakes F160, F164, F166 that engage a bisected sternum F162 attwo locations, and the retraction rakes F160, F164, F166 attach to theopposite ends of a swingletree F156, F170. A cable F154, F168 attachesto the mid-point of the swingletree F156, F170, and the swingletreeF156, F170 is free to pivot about this attachment. As seen in FIG. 48B,when the winch F158 pulls the swingletree F156, F170 upward, if one ofthe retraction rakes, such as F164, engages the margin of the incisionF162 first, then that retraction rake F164 is pulled downward, whichpulls the opposite retraction rake F166 upward until both rakes F164 andF166 engage the margin of the incision F162, where the swingletree F170has rotated with the right retraction rake F166 raised above the leftretraction rake F164. Force exerted by the cable F168, through theswingletree F170, and then through the retraction rakes F164 and F166pulls the bisected sternum F162 upward to provide surgical access forthe surgeon. The swingletree F170 here ensures that the forces on thetwo retractor rakes F164 and F166 remain equal—if the force on oneretraction rake, for example retraction rake F164, is larger, then theother retraction rake F166 is pulled upward until the forces on the tworetraction rakes F164 and F166 are balanced. More specifically, theswingletree F160, F170 rotates whenever the moment about the pivotingattachment to the cable F154, F168 become unbalanced. This occursautomatically. One drawback of the retractor F150 is that it requires alarge derrick-like arm F152 that is bolted to an operating table F153that suspends the winch F158 over the patient F163, or some similarsuperstructure over the operating table F153. Such structures canobstruct the surgical field, making access difficult from some angles,and present the risk of dropping the requisite fasteners into thepatient's open chest cavity.

A means for automatically adjusting the force exerted by each retractorelement without the large, table-mounted hardware of the retractor F150and with fewer actuators than the device of FIGS. 45A & 45B isdesirable.

FIGS. 49A and 49B illustrate one embodiment that balances the forces onmultiple retractor blades without table-mounted hardware and with feweractuators. This is a retractor F172 that uses a mechanical system forbalancing forces on the opposing arms of a Finochietto-style retractorin the prior art (see FIG. 44). Four retractor blades F184 engage themargins F202 of the incision to be retracted and create a surgicalaperture F200. Retraction is manually driven by rotation of the drivehandle F174 acting on rack-and-pinion drive F175 which moves along rackF176. There is a pair of blades F184 (also labeled F196 and F198 in viewF190 in FIG. 49B.1 and 49B.2, respectively) on each retraction elementF178 and F180 of the retractor F172. A first balancing assembly F186 iscomprised of two retractor blades F184 in each pair which are attachedto a balance bar F188, and the first balancing assembly F186 on thefixed retraction element F178 opposes a second balancing assembly F185on the moveable retraction element F180. Each balance bar F188 isattached to its respective retraction element F178 or F180 by a pivotingmount F187 or F189 so that the balance bar F188 is able to rotate in theplane of the page in FIG. 49A, but rotation of the balancing bar F188 inthe two planes perpendicular to the plane of FIG. 49A is not permitted.Prohibition of rotation in those other two planes permits the use ofrigid mounts to retractor blades, retraction hooks, or retractor rakes.In FIG. 49B.1, a balance bar F193 will rotate F195 about a pivot pointF194, and within the plane of the page, to balance forces F204 and F206on the two retractor blades F196 and F198 attached to the balance barF193, and will stop rotating F195 when the two forces F204 and F206 arebalanced. Additionally, should the two forces F204 and F206 again becomeunbalanced as retraction F212 proceeds, the balance bar F193 will,again, automatically rotate F195 the retractor blades F196 and F198 tobalance the forces F204 and F206 on the blades F196 and F198. In FIG.49B.2 depicts a subsequent state of view F190 showing a balanced statefor a pair of forces F208 and F210 during retraction F214, such thatF208 and F210 have equalized due to the accommodation via rotation F218of balance bar F216 about pivot point F217.

Referring now to FIGS. 50A through 50C, FIG. 50A shows how a balance barF226, F236 and F246 can be adjusted such that the balance bar F226, F236or F246 maintains an approximately constant ratio of forces F232, F242,F252 versus F234, F244, F254 between two retractor blades (not shown)located at the ends of the balance bar F226, F236 or F246. As shown inFIG. 50A balance bar F226 rotates, not due to an imbalance of the forcesF232 and F234 on the retractor blades, but due to an imbalance of momentM F227 about the pivot point F228. Thus, if the length L1 of a firstside of balance bar F226 is longer than the length L2 of a second sideof balance bar F226, then the force F₁ F232 on that first side will besmaller than the force F₂ F234 on the second side when the moment M F227is zero. Any ratio of forces can thus be accommodated. Additionally, thegeometry of the balance bar F226 determines a “righting moment”, amoment that returns the position of the balance bar F226 to neutral whendisplaced from neutral, and thereby makes the balance bar F226 “selfrighting.” As shown in FIG. 50B, the righting moment is determined bythe angle θ(θ=θ₁+θ₂) formed by lines L₁ and L₂ and by the length oflines L₁ and L₂. For example, the moment generated by F₂L₂ sin θ₂ ismaximal when L₂ is a long as possible and θ₂ equals 90°, and the momentgenerated by F₁L₁ sin θ_(□), is minimal when θ₁ equals 0° regardless ofthe length of L₁; therefore, the balance bar F236 will be maximallyself-aligning when θ equals 90° (see FIG. 50C). However, if a 90°rotation is not anticipated when the balance bar is used, then0=180°−2θ_(e) (θ_(e)=the maximum angle of rotation in use) provides thelargest righting moment.

As shown in FIG. 51, more than two retractor blades F270, shown as F270B₁, F270 B₂, F270 B₃ and F270 B₄, located on a retraction element F263,to be retracted in the direction F278, and another four retractorblades, shown as F272 B₁′, F272 B₂′, F272 B₃′, and F272 B₄′, located onthe retraction element F265 and to be retracted in the oppositedirection F280 can be placed onto each retraction element F263, 265 of aretractor F260. This is accomplished by tiering balance bars F262, F266and F267 onto which retraction blades F270 B₁ to B₄ are mounted and alsotiering balance bars F264, F268 and F269 onto which retractor bladesF272 B₁′ to B₄′ are mounted. Multiple tiers of balance bars arepossible.

FIG. 52 shows how retractor blade numbers that are not multiples of 2can be arranged so that the forces and moments still balance oneanother. As shown in FIG. 52 the force (not shown) generated by aretraction F300 on a blade F298 B₃ equals the combined forces (notshown) on two more blades F288 B₁ and F294 B₂. Similarly to that shownin FIG. 51, multiple tiers of balance bars are possible, including thosecreating uneven numbers of retractor blades. Again, all balance barelements will stop rotating when the moments about their respectivepivot points equalize.

Blades can be mounted to balance bars such that they are fixed orpivoting. As shown in FIGS. 53 and 54, balance bars can in someinstances also be mounted by a tensile element such as a cable, chain,or wire, permitting rotation out of the plane of the page in FIGS. 53and 54, similar to a swingletree. FIG. 53 shows in more detail aretractor F302 with retraction elements F306 and F308, a rack-and-piniondrive F305 with a drive handle F304, and four retractor blades F316associated with two opposing balance bars F310. The balance bars F310are connected to the retraction elements F306 and F308 by tensileelements, cables F312 and F314. Cables F312 and F314 permit easy,generous reorientation of the retractor blades F316 to forces andaccommodation of moments by the balance bars F310 while stilltransmitting the forces arising out of the motion F318 of the movableretraction element F308. FIG. 54 shows how multiple balance bars F338,F330, F340 can be tiered (similar to FIG. 51) by the use of chains F332,F334, and F336 attached by pivoting joint F324 on balance bar F338 andpivoting joints F328 on balance bars F330 and F340.

FIGS. 55A through 55C show a top view, a side view, and a front view,respectively, of another embodiment in which an entire retractor elementF348 is able to rotate around the axis of retraction F351; additionally,the retractor blades F362 are shaped like hooks that engage a rib F364to avoid damage to a neurovascular bundle (not shown), as described morefully in Section H. In FIG. 55A, the base element F350 of the retractorelement F348 is attached by a rotational joint F352 that allows theentire retractor element F349 to rotate out of the plane of the page inthe top view (FIG. 55A) and within the plane of the page in the frontview (FIG. 55C). Thus, rotational joint F352 permits the base elementF350 of the retraction element F349 to rotate within a planeperpendicular to the axis of retraction. Base element F350 attaches to afirst balance bar F354 by rotatable joint F358, and first balance barF354 attaches to second balance bars F356 by rotatable joints F358. Two(2) hook-shaped retractor blades F364 descend from each second balancebar F356. Rotational joints 352, or their equivalents, can be placed atevery rotatable joint F358 providing tremendous freedom of movement forthe balance bars F354 and F356 and the hook-shaped retractor bladesF362.

FIGS. 56A through 56C show a top view, a side view, and a front view,respectively, of an embodiment similar to that shown in FIGS. 55Athrough 55C, but an articulation F400 has been added to balance bar F354allowing it to bend to conform the balance bar F354 to a patient's ribF364 that curves in the plane perpendicular to the plane of the page asseen in the top view (FIG. 56A). Again, note that a cable, chain, orwire, as depicted in FIG. F54, could also permit rotation of the typeshown at rotational joint F352.

FIG. 57 shows a Finochietto-style retractor F430, similar to retractorF172 shown in FIGS. 49A through 49B, with an opposing pair ofswingletrees F437 and F439. Retraction elements F436 and F438 haveretractor arms F433 with articulations F434 that allow the retractorarms F433 to conform to the curve of a patient's body. Thesearticulations F434 could be passive, starting out with the retractorarms F433 straight and then conforming to the body when encountering thebody, or the articulations F434 could be preset by the surgeon andrigidly fixed in a patient-body conformal shape beforehand, or theycould be self-controlled via sensor feedback. The articulations F434might be formed as hinges, with two discrete sections interdigitating asshown in the FIG. 574, or the articulations F434 might be formed aselastomeric regions that bend smoothly from one section of a retractionelement to another. Another embodiment might possess retraction elementsF436, F438 which are continuously, smoothly flexible (along theirlength) in one plane, while rigid in the others.

FIG. 58 shows another embodiment of a retraction element F442 thatpermits more complex force distribution. Balance bars F443 and F445 forma second (child) tier F449 to a first (parent) tier F447, connecting atrotatable joint F446. Each balance bar F443, F448 has two retractionblades F448 attached by rotatable mounts F451. Balance bars F443 andF445 are overlapped at F450, presenting opportunities for generating abroader range of moment arms to distribute the pattern of forces alongthe margin of the incision. A broad range of overlap, bar length, andpivot position is possible; preferred embodiments arrange bar lengths,amount of overlap, and pivot positions so that all moments equalize, butthis need not be the case. Surgical situations may arise such that aclinician wishes to apply forces irregularly, for example if one isforced to simultaneously retract both exposed bone and soft muscle oradipose tissue in the same incision, or for example if a surgeon wishesto create a surgical aperture with purposefully nonparallel incisionmargins. Note also that besides varying the foregoing items in asurgical instrument design, the number of hierarchical levels is notrestricted. It may be advantageous to provide many ‘child’ levels ofbalance bars below the ‘parent’ level, forming a balance bar cascade ofarbitrary fineness, for example to ensure that dozens of tiny retractionhooks engage a patient's tissues, providing for nearly continuoussupport across the tissue face. Combining all four design variablespermits the design of retractors of arbitrary complexity that applyappropriate arrangements of forces in useful directions to a variety oftissues and anatomical structures without incurring tissue trauma.

FIGS. 59A through 59E show another embodiment of a retraction elementthat achieves automatic balancing of loads. Rather than using aswingletree, this retractor uses a cable F466 to transmit loads betweenretractor blades, posts, or hooks F468 that are mounted onto retractionarm units F462 by a rotational mount F460 formed by pin F470 whichattaches retraction hook F468 to retraction arm unit F462. FIG. 59Ashows a side view showing one retraction hook F468 attached to aretraction arm unit F462 by a rotatable mount F460. The retraction hookF468 engages a rib F456, directly against that bone, such as in athoracotomy. The cable F466 attaches to the retraction hook F468 bypassing through a hole F480 in the shaft F469 of the retraction hookF468. FIG. 59B shows a front view, with three retraction hooks F468attaching to the retraction arm unit F462. The retraction arm unit F462has two articulations F474, permitting the retractor arm units F462 toindependently align to the curvature of the rib. Optionally, theretractor arms can be solid, without articulations F474. Referring toFIG. 59B, the cable F466 attaches at one end to a retraction elementF462 and then courses through the holes F480 in the retraction hookshafts F469 and over pins F464 in the retraction arm units F462;finally, cable F466 attaches at its other end to a capstan F478 used toadjust the tension of the cable F466, and thereby adjust the magnitudeof the swinging of the retraction hooks F468. FIG. 59C shows a top view,illustrating how the cable F466 travels from an attachment F482 at oneend, then zig-zags left to right, back and forth as it passes from holesF480 in the shafts F469 of the retraction hooks F468 to pins F464 insiderecessed holes in the retraction arm units and finally to a capstanF478. Thus, as illustrated in FIG. 59D, when a first retraction hookF468 is pushed (by the tissues at the margin of the incision) toward theleft, it tensions the cable F466, which then pulls a neighboringretraction hook (F468′) to the right. This repositioning of theretraction hooks F468 and F468′ will continue until the force on bothretraction hooks equalizes. Again, changes in the position of thethrough hole F480 in the shaft of the retraction hook F468 and F468′will control the ratio of forces between those retraction hooks. FIG.59E shows how the articulations F474 between retraction arm units F462permit the retraction arm units F462 to conform to the curvature of thepatient's body.

FIGS. 60A and 60B show a physical model of a retractor F540 of the typedescribed in FIG. 59A through 59E. FIG. 60A shows a top view of theretractor F540, and FIG. 60B shows an oblique side view of the retractorF540, showing the retraction hooks F558 (similar to F468) and cablesF556 (similar to F466). Paired retraction elements F544 are attached toand ride along a dual-thrust lead screw F546. Rotation of thedual-thrust lead screw F546 with respect to the retraction elements F544causes the retraction elements F544 to move F548 apart for retraction orback together for closure. The retraction elements F544 havearticulations F552, like articulations F464 in FIGS. 59A-59E. Retractionhooks F558 are attached to the retraction elements F544 in the samemanner as described in FIG. 59. The retraction hooks F558 are rotatableabout their long axes, such that prior to insertion into an incision tocreate a surgical aperture, a surgeon can first align the hook-shapedtips of the retraction hooks F558 all pointing parallel to the directionof the incision (and so parallel to the margins of the incision, makingthat part of the retractor F540 that actually descends into the patientas thin as possible) for easy insertion into the incision and then,secondarily, the surgeon can rotate the retraction hooks F558 such thatthe hook shapes swing out and under the ribs adjacent to the retractionelements F544 (on the left and right side, respectively) to engage theribs for retraction. Margins F555 of the two retraction elements F544can be shaped such that the retraction hooks F558 on one retractionelement F544 interdigitate with the retraction hooks F558 of theopposing retraction element F544, decreasing the separation of the axesof the retraction hooks F558 to zero when they are inserted into theincision. FIG. F60B shows the retraction hooks F558 aligned in thisinstance parallel to the direction of the incision; the retractionelements F544 here have been somewhat differentially rotated about thedual-thrust lead screw F546 to make it clear how the shape of the marginF555 of the retraction elements F544 can be sinuous, permitting theinterdigitation of the left and right retraction elements F544.

FIG. 61 shows another embodiment of a retractor F560 that achievesautomatic balancing of loads. Multiple retractor blades F566 are mountedonto hydraulic cylinders F573 having pistons F572 that move in responseto pressure F567 in the hydraulic cylinder F573, and the hydrauliccylinders F573 are fluidically F569 connected by hydraulic interconnectsF574 and arrayed in opposing gangs 570 of hydraulic cylinders F573. Thegangs F570 of hydraulic cylinders F573 are positioned on a fixedretraction element F562 and a moveable retraction element F564 of aFinochietto-style retractor driven by a handle F568. When, for exampleduring retraction, the tissue resistance force on an arbitrary firstretractor blade F566 draws out the first retractor blade F566 such thatthe first hydraulic piston F572 to which that the first retractor bladeF566 is attached is also pulled a portion of the length of hydraulicpiston F572 out of the first hydraulic cylinder F573, then the pressureF567 inside the first hydraulic cylinder F573 decreases. This decreasein pressure F567, communicated to the other hydraulic cylinders F573 viathe hydraulic interconnects F574, causes internal fluid F569 to flowinto this first hydraulic cylinder F573 from the other hydrauliccylinders F573. Flow of the internal fluid F569 out of the otherhydraulic cylinders F573 decreases their internal pressures F567consequently pulling the other hydraulic pistons F572 inward, so causingthe other retractor blades F566 attached to the other hydraulic pistonsF572 to move F576 in a direction opposite that of the first retractorblade F566. As with the embodiments above, the ratios of forces betweenall the retractor blades F566 can be designed to be any ratio desired,for example by the use of hydraulic cylinders F573 with different radii.In another embodiment, the hydraulic cylinders F573 can be a singlehollow fluid-filled housing with four pistons (or other number ofpistons) emitting from the housing, with the housing acting as a fluidicplenum keeping all four pistons in hydraulic communication. Thehydraulic fluid in these systems can be oil, sterile water, sterilesaline, or a gas, such as air. Air further provides compressibilitywhich acts like a “spring” in such a system, enabling complianceappropriate when loading tissues, for example.

FIG. 62 shows another embodiment of a retractor F580 that achievesautomatic balancing of loads with hydraulics. Similar to the cableddevice depicted in FIGS. 59A through 59E, retraction hooks F584 and F586are attached to retraction elements F582 by rotatable mounts F588;however, now the cables are replaced by a series of hydraulic cylindersF590 that compress or elongate (i.e., change total length) as theretraction hooks F584 and F586 rotate about the rotatable mount F588.The hydraulic cylinders F590 are fluidically connected at fluidicconnection F599, so as one hydraulic cylinder F590 is elongated, forexample, it pulls hydraulic fluid F591 from the other hydrauliccylinders F590, causing them to shorten. Thus, as shown in FIG. 62, as afirst retraction hook F584 is pushed to the left (movement F594),causing this first retraction hook F584 to rotate clockwise about therotatable mount F588, the hydraulic cylinder F590 of retraction hookF584 elongates, making the other hydraulic cylinders F590 (such as thatassociated with the second retraction hook F586) shorten, therebyrotating second retraction hook F586 counter-clockwise about therotatable joint F588, making second retraction hook F586 move to theright (movement F592). Alternatively, the hydraulic elements F590 andF599 can be arranged to be compressed under load instead of pulled,driving fluid F591 out of the hydraulic cylinder F590 of the first(engaging) retraction hook F584 and into the hydraulic cylinder F590 ofthe second (reacting) retraction hook F586.

FIGS. 63A through 63E show another embodiment or a retraction elementF608 with retraction posts F602 that compensate for one another's motionvia retrograde action. Fenestrated bars F604 link retraction posts F602,and motion of one retraction post F602 causes the other retraction postsF602 to adjust via a mechanical linkage through fenestrated bars F604.FIG. 63A shows a model with the fenestrated bars F604 mounted on afulcrum F606 and the retraction posts F602 passing through thefenestrated bars F604 via holes F605, with the counteracting offsets ofthe retraction posts F602 being evident. FIG. 63B shows a top view andFIG. 63C shows a side view of a retraction element F608. Eachfenestrated bar F604 in this example possesses two holes F605 throughwhich pass two retraction posts F602. Each fenestrated bar F604 thenfurther possesses one more hole F631 admitting a fulcrum pin F630,forming the fulcrum F606 upon which and about which the fenestrated barF604 is free to rotate. The fenestrated bar F604 resides in this exampleclose to the base of the retraction arm F612, to which each retractionpost F602 is connected via a hinge F632 which allows each retractionpost F602 to swing back and forth along the axis of retraction F639.FIG. 63D shows the action for one retraction element F608. Consider themiddle retraction post F602 and its two fenestrated bars F602. As a themiddle retraction post F602 gets pushed backwards by the impingingtissue, the middle retraction post F602 moves backwards, and this motionis transmitted as a moment by both fenestrated bars F604 around thefulcrum F606 to the top and bottom retraction posts F602, pushing thatthe top and bottom retraction post F602 forward to meet the oncomingtissue. As with some of the other embodiments disclosed above, themotion of the retraction posts F602 ceases when the moments equalize.FIG. 63E shows the counter motion of that shown in FIG. 63D. Thisembodiment possesses two fenestrated bars F604 that together link themotions (and so the countermotions) of three retraction posts F602. Notethat one may design the fenestrated bar system with an arbitrary numbern of fenestrated bars linking n+1 retraction posts. Note also that onemay combine fenestrated bars of arbitrary lengths and proportions socreating useful variations of motion of the retraction posts withoutdeparting from the intent of the present invention.

FIGS. 64 through 66B show still another embodiment of a retractionelement of the current invention, this time providing swingletrees withthe ability to automatically, dynamically and continuously adjust theposition of their pivots to accommodate changing loads. In all FIGS. 64through 66B the direction of retraction would be “up” towards the top ofthe page, and the patient's tissues would thus react by pulling “down”towards the bottom of the page. The retractor blades shown in FIGS. 64through 66B thus engage an incision along the bottom of the page.

FIG. 64 A shows retraction element F700 having a rectractor arm F702that is used to pull up in the direction of retraction F701 F722. Atwo-tiered assembly of swingletrees, comprised of first swingletree F704(“parent swingletree”) and second swingletrees F706 (“childswingletree”) hold four (4) retractor blades F708. First singletree F704attaches to retractor arm F702 via pivot F710, here shown as a sheave.Second swingletrees F706 attach to first swingletree F704 also via pivotF710, here shown as a sheave. Retractor arms F708 attach to secondswingletrees F706 via a pivot point F712, here shown as a rotating mountformed by a pin and a bushing. Swingletrees F704 and F706 still pivotwithin the plane of the page about a pivot F710 that acts as a fulcrum,shown here as a freely rotating sheave.

FIGS. 65A through 65C show side views of two different embodiments ofretraction element F700. FIGS. 65A and 65B show side views of theretraction assembly F700 shown in FIG. 64. FIG. 65C shows anotherembodiment of retractor assembly F700 that captures first swingletreeF704 and second swingletree F706 such that the assembly is heldtogether. The sheave F720 at pivot F710 can be a bearing-mounted roller.As shown in FIG. 65B, the sheave F720 includes a provision (such as agroove F722 or channel around its rim) for cupping, nestling, or ridingalong and otherwise retaining its association with that edge F724 ofeach swingletree F704, F706 that is closest to the incision. The firstand second swingletrees F704 and F706, respectively, includes aprovision so that it mates with the sheave F720. As shown in FIG. 25B,the lower edge F724 of swingletrees F704, F706 can be convexly radiusedand otherwise shaped to accept the concavely shaped groove F722 of thesheave F720. Given this arrangement, the lower edge F724 of swingletreesF704, F706 ride in the groove F722 of the sheave F720, such that theloading by the patient's tissues retraction actually seats theswingletrees F704, F706 more securely in the sheave F720.

FIG. 25C shows another embodiment of the retractor assembly F700, herelabeled as retractor assembly F730. To avoid swingletrees F704,F706disengaging from sheaves F722, first swingletree F704 is mated withanother swingletee F732, creating a stacked assembly with two sheavesF722 connected to each other by a pin F732 through retractor arm F702.First swingletrees F704, F732 are thus captured by retractor arm F702,and second swingletree F706 is thus captured by doubled firstswingletrees F704, F732. Another means of capturing each swingletreeF704, F706 is to have sheave F720 ride in a restrictive slot formedwithin the child swingletree bar, instead of riding along the lower edgeof the swingletree.

A “child” swingletree (e.g., second swingletree F706) can serve as the“parent” of other swingletrees (in this case, F676 and F677) lower downin the hierarchy, creating as many levels as desired. Properly sized andassembled, such a network of swingletrees automatically assures so thatno excess or imbalance of forces can remain. In this way, any excessforce applied against the tissue of the patient is reduced.

One problem with retractor blades and the like is their tendency toapply not only forces directly against the tissue of the patient, but toshear along (or roughly parallel to) the raw surface of the incision. Asa retraction proceeds, the relative motion or loading of the retractorblades may induce sliding along the edge of the margin of the incision(or an attempt by one or more retraction elements to do so), shearingthe tissue in that plane (or tearing it outright).

FIGS. 66A and 66B show another embodiment that uses distributedcurvature of the freely riding swingletrees to limit this shearingmotion of the retractor blades. FIG. 66A shows a retraction assemblyF740 having swingletrees with tightly curved arms that make retractionassembly F740 more prone to shearing of the retractor blades, and FIG.66B shows a retraction assembly F760 having swingletrees with moregently curved arms that that make retraction assembly F760 less prone toshearing of the retractor blades. The local curvature of the swingletreesurface (riding in the parent sheave) influences the magnitude of theshear applied by rectractor blades F712 along the surface of theincision (i.e., the behavior of the swingletree hierarchy is a functionof the curvature of the swingletrees comprising it). Consider FIG. 66A,swingletrees F742 and F744 are shaped with a substantially highcurvature near the center of the swingletree, and lower curvature neartheir tips; thus, sheaves F720 experience strong centering forces F748and remain more tightly centered under load, behaving much (but not all)of the time as if the pivots F710 formed by sheaves F720 were simplydrilled through the bodies of the swingletrees. Under this circumstanceshear is more likely to develop along the surface of the incision.Consider now FIG. 66B with swingletrees F762, F764 shaped with a muchgentler distribution of curvature along the swingletree bar, then thecentering forces F768 are smaller. Shear is instead relieved as thepivots F710 of the swingletrees F762, F764 can more easily shiftlaterally to suit owing to the smaller centering forces F768. Ideally,shear applied to the margin of the incision is minimal and the pivotsF710 supporting a given swingletree F762, F764 remain substantially nearthe center of its respective swingletree F762, F764, thereby allowingthe swingletree to rotate about the axis of the pivot F710, and withinthe plane of the page, to accommodate irregular loading as before. Thegently curved swingletrees F762, F764 thus permit simultaneousaccommodation of rotation and sliding, thereby eliminating bothexcessive forces and shear.

Note that the intersection between the parent sheave and the childswingletree can be formed of two smooth surfaces, or it could be formedlike a rack-and-pinion, where the parent sheave is a toothed like apinion gear and the mating lower surface of the child swingletree bar isa toothed rack. Given this, one could further arrange for the activesensing and actuator control of the sheave rotation such that theposition of the child is influenced by the active rotation (orclutching) of the sheave. This example admits active modulation of theplay of forces and moments through a swingletree cascade. In someinstances it may prove advantageous to apply shear on purpose, or toimbalance the forces applied to the patient's tissues, according to theneeds of the surgeon.

G. Reducing Inappropriate Forces G.1 Forces Exerted by Retractors onTissues

When a surgeon performs a thoracotomy, she must deform a patient's bodywall to move the apposed ribs aside far enough to permit her hands toaccess the thoracic cavity (see FIG. 67). Current medical practicedictates that a surgeon (1) makes an incision between and parallel totwo apposed, adjacent ribs; (2) simultaneously inserts the opposingblades of a rib spreader, or “retractor”, into the incision; and (3)turns the crank to force open the opposing blades, and the ribs,creating a hole. The hole or surgical “aperture” is typically about 10centimeters across, and can range from 5 cm to 20 cm. Modern retractorsare essentially rigid metal devices sporting hand-cranked jack elements.Today's spreaders, such as Finochietto-style retractors (see FIGS. 2 and68A) are typically rack-and-pinion devices that, while constructed ofpolished stainless steel, operate on simple mechanical principlessimilar to those of 2,000-year-old bronze medical instruments found inancient Greece (a vaginal speculum, see FIG. 68B), that is, ahand-cranked jack driving projecting blades. The retractor shown inFIGS. 2 and 68A are widely used; this retractor uses a lockablerack-and-pinion crank, as first disclosed by Finochietto in 1936 andpublished in 1941 (Bonfils-Roberts 1972). The principle remains the sameas the ancient ones: equip a frame, otherwise rigid in all directionsand along all axes, with the ability to expand along a single axis tosimply overpower the tissues to force access to the inside of thepatient's body. Thus, referring now to FIG. 69, the force required foropening is considered to be simply opposing forces F₁ G8 and F₂ G10,applied at two points P₁ G12 and P₂ G14 lying on a single line ofaction. The only accommodations for more complex forces provided by theprior art are curved retractor blades, providing for example, non-pointloading such as on a Cooley retractor G16 (FIG. 70A), and swivelingretractor blades such as on older retractors that are no longer used(e.g. the retractors of Sauerbruch G18 (FIG. 70B), De Quervain G20 (FIG.70C), and Meyer G22 (FIG. 70D). Archeological museums and currentmedical supply catalogs visibly demonstrate that this one-dimensionalthinking has underlain retraction device design for millennia.

Retractors work—they do force open bodies, but their design does nottake into account the complex loading regime imposed on (and, inreaction, by) the patient's body. The result is that today's patient'stissues are bearing substantial loads that are not directly related to,or required for, opening; therefore, these retractors are causingunnecessary tissue trauma.

The inventors have measured forces during thoracotomy and observed forthe first time that the actual forces of retraction are not the simple,one-dimensional case depicted in FIG. 69. It can now be appreciated thata complex set of forces and torques interact on the retractor, and thuson the patient's tissues. There are two lines of evidence for thisclaim. First, the force on a retractor (see FIG. 71, discussed below) isusually sufficient to lift the body of the retractor off the patient'sbody, such as in FIG. 67. Second, our measurements reveal that theforces acting on opposing retractor arms are not the same. FIG. 72 showsour new data that were collected with the retractor shown in FIG. 12,which is fitted with a computer-controlled stepper motor B8 to providesmooth motion and with a linear potentiometer B16 to measure thedistance of separation of the retractor blades B20 and with straingauges on the retractor blades B20 to measure the forces on each of thetwo retractor blades B20. This retractor was used to performthoracotomies on the carcass of a pig. In the retraction shown in FIG.72, retraction occurred over 6 minutes, starting at 10 seconds, with atwo-minute pause in retraction from 70 seconds to 190 seconds. Thedifference in the forces G64, G66 measured on the two retractor bladesis maximal at the end of retraction (at time=480 seconds, 19.5 kg versus16.0 kg, a difference of about 20%). These force measurementsdemonstrate that retractors in the real world do not behave like perfectforce diagrams out of a physics book as shown in FIG. 69, with twoendpoints of zero extent (and equal force) connected by aone-dimensional line.

Applying pure tension or compression with today's retractors seemsimpossible. In light of the observations and measurements presented inFIGS. 71 and 72, it is difficult to imagine that one could ever seeequal forces acting on the two blades of a conventional retractor placedinside a real patient.

Why is this so? Refer to FIG. 71. First, retractors such as retractorG24 possess significant mass that is distributed unevenly, and they haveblades G33 and G31 with non-zero dimensions and corners. Second, thepatient's body is a sculpturally and structurally complex composite ofheterogeneous biomaterials. Every structure inside a patient (examplee.g., ribs G26 and G28) is anisotropic and almost nothing behaveslinearly. When the blades G31 and G33 of the retractor G24 engage thetwo sides of an incision, the body forcefully opposes motion of theblades G31 and G33. The patient's tissues (e.g., ribs G26 and G28) grewand developed alongside each other and the forces they generate tend torestore their apposed relationships. While the retractor G24 drives itsretractor blades G31, G33 apart in a straight line, such as displacementG32 and G30, the there are numerous forces G36, G38, G40, G42, G52 G56and G58 and torques G27, G34, G44, G46, G48, G50, G54 and G60 acting onthe retractor blades G31 and G32 that arise from the deformations of theheterogeneous, three-dimensionally complex tissues surrounding theincision. Consequently, these forces are similarly three-dimensional andcomplex.

In the act of forcing open a living body with a conventional retractorG24, first one corner of one of the inserted retractor blades G31 willstrike some part of a rib G26 and settle onto that rib G26 and theintervening muscle tissue in an irregular fashion. Once that happens,and since the retractor G24 is a rigid object, the retractor G24 willreact to the first contact, shifting position, until the other retractorblade G33 encounters and settles somewhere onto its own opposing rib G28and muscle. The retractor G24 then reacts and shifts again, with theblades G31, G33 sliding along and shearing muscle against bone, back andforth in concert, as the surgeon applies torque to the retractor handleG35 (and so the entire retractor) as the patient's body forcefullyopposes motion of the retractor blades G31, G33. All the while, thepatient's body deforms unevenly under the loads imposed by the retractorG24. The structures of the patient's body are deforming, which affectsre-seating of the retractor blades G31, G33, which affects thedeformation of the body, and so forth. All elements are shifting atonce, but not evenly (i.e., not rectilinearly). The retractor G24 isessentially a rigid object; at any time, there is little or no provisionfor the complex mechanical behaviors that are the hallmark of livingtissue. Because of this, and crucially, the retractor blades G31 and G33apply uneven forces to the body throughout spreading, and the forces areuneven when the surgeon achieves the required opening.

The apparent intention of the designers of conventional retractors wasto apply large forces along a single line of action (the “retractionaxis”). However, they do not accomplish this because they do notconsider the response of the patient's body. The forces on the retractorare those imposed by the reaction of the patient's body to thedisplacement of its tissues, and the patient's body does not respondalong a single line of action—it generates complex, three-dimensionalforces in response to deformation. Furthermore, these forces change asdeformation proceeds while the retractor remains in contact with thepatient's body tissues. The retractor, in return, opposes these forcesby moving (e.g. lifting off of the patient's body) or by accumulatingstresses in the retractor. Consequently, the patient's tissues bearsubstantial stresses beyond those required for opening, leading totissue trauma (e.g., broken ribs) that, otherwise, should be avoidable.

Clearly, minimizing undue stresses during a thoracotomy or othersurgical procedure would be beneficial to the patient, reducing tissuetrauma to the barest minimum required to generate an adequate surgicalaperture. This can be accomplished by (a) generating force along a lineof action to retract the tissues to achieve a desired surgical opening(the “retraction axis”), (b) accommodating motions (e.g. translationsand rotations) of the retraction axis such that there is minimalopposing force from the retractor to these motions, and (c)accommodating motions (e.g. translations and rotations) of the retractorblades, and of the underlying tissues, that are not parallel to theretraction axis such that these non-parallel motions occur with minimalopposing force from the retractor. To this end, the retractor shouldalso be as lightweight as is practicable. Thus, the retraction axis isfree to move in space and there is minimal force opposing motions not onthe retraction axis.

This can be accomplished by a lightweight retractor that is free tomove, or its parts are free to move, as the patient's body exerts forcesthat are not along the retraction axis. Such a retractor, thus,automatically aligns itself (e.g., its blades) such that the retractionaxis is always oriented along a direction that achieves the desiredsurgical opening while reducing the magnitudes of all forces.

Disclosed herein are apparatus and methods for automatically minimizingthe imposed deformation forces applied to the patient to the minimumrequired for surgical access. With the various embodiments of thepresent invention one can readily apply forces sufficient to deform thepatient's tissues in the manner appropriate for medical procedures whileminimizing forces arising from or leading to undesired deformations ofthe patient's tissues.

G.2 Swing Blade Retractor—Dual-thrust Lead Screws

FIG. 73 shows one embodiment of a retractor G68 that possesses a newdegree of freedom of motion, allowing the retractor blades G76 toautomatically realign to reduce forces that are not parallel to theretraction axis. Retractor G68 is functionally divided into three units:a dual-thrust lead screw G80, a first retraction unit G70, and a secondretraction unit G72. Collectively, retractor G68 is referred to as a“Swing Blade Retractor”. The dual-thrust lead screw G80 is a lead screwhaving at least left-hand threads on one end and right-hand threads onthe other end (such as those offered by the Universal Thread GrindingCompany, Fairfield, Conn.).

Each retraction unit G70, G72 is comprised of a retraction body G78, G79having hollow ‘female’ threads that engage the outside surface of thedual-thrust lead screw G80, a retractor arm G74, G75, and a retractorblade G76, G77. The retraction bodies G78, G79 have either a left-handthread or a right-hand thread with which to follow the travel of thethreads on the outside of the dual-thrust lead screw G80. When thedual-thrust lead screw G80 is rotated, the dual-thrust lead screw'sthreads (which are engaged with the threads in the retraction bodiesG78, G79) force the two retraction units G70, G72 to move away from eachother to displace the (now formerly) apposed tissues. Rotation of thedual-thrust lead screw G80 about its long axis can be accomplished byany of several means, including a hand crank mounted to one end of thedual-thrust lead screw G80, a motor mounted to one end, a hand crankattached to a gear inside one retraction body unit G78, or a motorattached to a gear inside one body unit (or both). The gears might behelical gears, crown gears, friction drives, or other means permitting aretractor body to simultaneously drive dual-thrust lead screw G80rotation and follow the motions of the threads on the outside of thelead screw.

Note that a dual-thrust lead screw G80 could be made to have anarbitrary number of regions of both left- and right-handed threads, witharbitrary pitches (and so advance ratios), such that a plurality ofretraction units G70 could be made to move all at once on a single leadscrew G80, at different speeds and directions relative to one another.For example, one might wish to engage more than two ribs at once, say,four or six, and move them all in concert to distribute deformations andloading, and to prevent crushing of soft tissues between sequential setsof ribs.

While away from the body of the patient and not locked together, each ofthe Swing Blade Retractor's G68 retraction units G70 and G72 is able toswing freely about the long axis of the dual-thrust lead screw G80. Notethat rotation of both retraction units G70, G72 about the long axis ofthe dual-thrust lead screw G80 is constrained when the Swing BladeRetractor G68 is placed against the patient's body or if the retractorblades G76 and G77 are engaged with the tissues. The result of thisconstraint is that when the dual-thrust lead screw G80 rotates, whileboth retractor blades G76 and G77 are against or inside the patient'sbody, both retraction units G70 and G72 move apart, opening the incisionto create the surgical aperture. Furthermore, if a crank or motor isplaced inside one retraction body G78 or G79 of only one retraction unitG70 or G72, respectively, then both retraction units G70 and G72 stillmove apart under rotation of the dual-thrust lead screw G80. Theretraction units G70 and G72 will come back together when thedual-thrust lead screw's G80 direction of rotation about its own longaxis is reversed. Thus, a motor or crank in one retraction body G78 ofone retraction unit G70 can be used to rotate the dual-thrust lead screwG80 and, thereby, drive both retraction units G70 and G72 apart.

FIG. 74 depicts how a Swing Blade Retractor G68 has an additional degreeof freedom, relative to a conventional retractor, such as those shown inFIGS. 67, 68A, 68B, and 70A through 70C. For the Swing Blade RetractorG68, retraction units G78, G79 are mounted to the dual-thrust lead screwG80 only by the threads in each retraction body G78, G79, so theretraction units G78, G79 are free to rotate about the long axis of thedual-thrust lead screw G80. The retractor blades G76, G77 are, thus,able to rise and fall in a direction G98 approximately perpendicular tothe axis of retraction G100 and perpendicular to the surface of the bodyof the patient (i.e., in and out of the incision). In contrast, the armsof a conventional retractor are always constrained to move towards oraway with respect to one another within that single axis of retraction;any tendency of the retractor blades to move in any other direction isstrongly resisted by the substantial structure of the retractor.Importantly, any tendency of the body wall in contact with the retractorblades to move in some direction other than the axis of retraction isalso resisted by a conventional retractor, and, subsequently,substantial stresses can form in the body's tissues that are unrelatedto the force required to obtain the surgical opening. In other words,the minimum amount of force and/or trauma to open the body wall mightrequire a curved path, or a slightly shifting path, as opposed to aunidirectional, rectilinear path.

An additional advantage of a Swing Blade Retractor is that it can assistinsertion of the retractor blades into the incision during preparationfor retraction. When inserting the retractor blades of the prior artinto an incision through a patient's body wall, the surgeon is forced,by the rigidity of the retractor frame, to jam both retractor blades inat once. This is a problem because this cannot be done until the surgeonfirst uses her fingers to pry open the incision to be wide enough to beable to fit in both blades, which may themselves have wide edges.However, for the Swing Blade Retractor G68, because the two retractionunits G70, G72 swing freely and independently, each retractor blade canbe inserted one at a time as desired, allowing a surgeon to begin with asmaller opening.

Another advantage of the Swing Blade Retractor G68 is that the hollowthreads of the retraction bodies G78, G79 can be formed of more than onepiece. For example, the hollow threads can be made of two halves, each asemi-circle in section, that are brought together inside the retractionbody G78, G79 to enclose, embrace and engage the threads of thedual-thrust lead screw G80. This enables another improvement over therack-and-pinion retractors, which must be laboriously cranked back allthe way shut to be removed, in that one or both of the Swing BladeRetractor's G68 retractor bodies G78, G79 can be instantly removed fromthe dual-thrust lead screw G80 by disengaging the two-piece hollowthreads. For example the two-piece hollow threads can separate such thatthe dual-thrust lead screw G80 can pass through a gap made by theseparation. The means of thread disengagement might be a button, lever,motor or flap that when closed retains and stabilizes the threadedhalves around the dual-thrust lead screw G80. This enables the surgeonto rapidly lift one or both retraction bodies G78, G79 away to clear thesurgical field in an emergency, facilitating removing the entireretractor G68. Similarly, the hollow threads, rather than being composedof two halves that fully or almost fully wrap the dual-thrust lead screwG80, can engage only one side of the dual-thrust lead screw G80,wrapping only ⅕th, for example, of the circumference of the dual-thrustlead screw G80. This facilitates disengagement of the threads from thedual-thrust lead screw G80—the threads need only be lifted away from thedual-thrust lead screw G80 to permit free motion of the retraction unitG70, G72 along the length of the dual-thrust lead screw G80.

The advancement of the retraction bodies G78, G79 usually proceeds fromthe rotation of the dual-thrust lead screw G80 about the dual-thrustlead screw's G80 long axis. The rotation of the dual-thrust lead screwG80 can be the result of a source of torque such as a hand crank, amotor, or the like. The source of torque can be external to theretraction body G78, G79. In one embodiment, the source of torque islocated inside one retraction body G78 or G79. In this case, theretraction body G78 or G79 thus possesses its normal capability to bedriven along the dual-thrust lead screw G80 while simultaneously beingthe agent that drives the rotation of the dual-thrust lead screw G80about its own long axis. For example, one may modify the dual-thrustlead screw G80 by further providing rotation means co-located with thethreads along the shaft so that the retraction body G78 or G79 mayengage both the threads for advancement and the rotation means forrotation. One example of rotation means would be splines cut along thelength of the shaft. The threads of the dual-thrust lead screw G80 andsplines (not shown) can co-exist on the same driveshaft, are notmutually exclusive, and can be engaged by separate mechanisms housedwithin the retraction body G78 or G79. The hollow threads disclosedabove can provide the engagement for advancement upon rotation of thedual-thrust lead screw G80, while a toothed ring drive (not shown)surrounding the lead screw but engaging only the splines provides therotation. The hollow threads “see” only the threads of the dual-thrustlead screw G80 while the toothed ring “sees” only the splines, i.e., thesurface gaps forming the splines do not present occlusions to thethreaded follower and the surface gaps forming the threads do notpresent occlusions to the toothed ring drive. This form of thedual-thrust lead screw G80, called a splined dual-thrust lead screw, canbe made by first cutting, machining, or rolling helical threads into aplain metal rod or cylinder, and then cutting splines in the samecylinder. Other means are possible, but the intent is to provide in onedevice (and even in one component of the device) simultaneousdual-thrust lead screw G80 thread following and lead screw rotation.

Another benefit of the Swing Blade Retractor G68 design is that it isself-aligning. For stability's sake, the Swing Blade Retractor G68exploits the tendency of the edges of the patient's body wall tore-appose once separated. When a surgeon retracts the body wall, theapposed or touching edges of the incision now move apart. The body'smechanical reaction is to re-appose the edges of the incision, i.e., thedistance between the edges of the incision “tries” to return to zero.Crucially, this re-apposition occurs in three dimensions. No matter theinitial orientation of the retractor blades G76, G77, they cannot swingapart once engaged with the patient's body wall; thus, the naturalforces at work in the patient's body automatically align the retractorblades G76, G77 (and indeed, the entire axis of retraction G100) toexactly that angle in three dimensions that minimizes the distancebetween the retractor blades G76, G77, and so, the force required forretraction.

G.3 Swing Blade Retractor—Roller Drives

FIG. 75 shows another means G104 for driving retraction units in aretractor. Rather than using a dual-thrust lead screw, a roller driveG106 is used. A roller drive combines thrust and rotation, like adual-thrust lead screw, but can be more efficient, and it offers theability to variably adjust the pitch of drive. Roller drive G106 hasthree or more rollers G110 engaging a shaft G114 with at least one ofthe rollers, a driver roller G112, coupled to a torque source, such as amotor or a hand crank, and with the other rollers G110 acting as idlerrollers which passively roll along the shaft G114. The rollers G110 andG112 can have collars that help guide the rollers G110 and G112 alongthe shaft G114, ensuring that the rollers G110 and G112 remain engagedwith the shaft G114. The shaft G114 can be substantially rectangular incross section, as in FIG. 75, or shaft G114 can have any othercross-sectional shape matched to the rollers G110 and G112. The rollersG110 and G112 are forced against the shaft G114 such that frictionbetween the driver roller G112 and the shaft G114 causes the driverroller G112 to impel the shaft G114 when the driver roller G112 rotatesunder the action of its torque source. Note that motion is relative, sothe roller drive G112 can move along a stationary shaft G114, or a shaftG114 can be pushed by a stationary roller drive G112. The rollers G110and G112 can be fitted with appropriate bearings to permit substantialforce pushing the rollers G110 and G112 against the shaft G114 togenerate substantial friction between the shaft G114 and the driverroller G112. The rollers G110 and G112 can be forced against the shaftG114 either by precise manufacture of the mounts holding the rollersG110 and G112, or the rollers G110 and G112 can be pressed into positionby, for example, a cam that variably moves the rollers G110 and G112away from the shaft G114, releasing the shaft, or presses rollers G110and G112 against the shaft G114 to hold or drive the shaft G114.

FIG. 76 shows how a roller drive G106 can be used in a retractor G116.Retraction unit G117 has a roller drive comprised of a first idlerroller G120, a second idler roller G121, and a drive roller G124. Idlerrollers G120, G121 and drive roller G124 engage shaft G122, and torqueon drive roller G124 drives retraction against the retraction force G126from the tissues. This configuration of idler rollers G120, G121 anddrive roller G124 provides several advantages. First, retraction forceG126 results in a torque G118 on retraction unit G117 that then appliesa force G128 on the drive roller G124 and the first idler roller G120that increases drive friction for drive roller G124, thereby improvingengagement between the driver roller G124 and the shaft G122. Second,the shaft G124 is smooth, decreasing chances for snagging items in thesurgical field. Fourth, the rollers G120, G121, and G124 and shaft G122are easier to manufacture precisely, decreasing cost.

FIG. 77 shows another embodiment of a roller drive G130. The idlerrollers G138 and drive roller G139 do not have collars as in FIGS. 75and 76; rather, the idler rollers G138 and are circular cylinders. InFIG. 77, the shaft G136 is circular in cross-section. The rollers G138have an axis of rotation G140 defining the orientation of rotation G142of the rollers G138. On the left-hand side of FIG. 77, the rollers G138and shaft G136 are configured such that the roller axes of rotation G140are all perpendicular to the long axis of the shaft G136; thus, when thedriver roller is actuated, the shaft moves out of the page plane (seerotation-indicating arrows). On the right-hand side of FIG. 77, theroller axes of rotation G140 are aligned oblique to the long axis of theshaft G136; thus, when the driver roller G139 is actuated, the shaftG136 moves helically out of the page plane. In other words, the motionof the shaft G136 imparted by the rollers G138 and G139 has twocomponents, one that translates the shaft G136 out of the page plane andone that rotates the shaft G136 around the long axis of the shaft G136.

FIG. 78 shows that the relative degree of each motion of the shaft(translation and rotation) is determined by the angle between the rolleraxis of rotation G140 and the long axis of the shaft G136. The anglebetween the roller axis of rotation G140 and the long axis of the shaftG136 is shown to vary from left to right in FIG. 78. On the left-hand ofFIG. 78, the roller axis of rotation G140 is perpendicular to the longaxis of the shaft G136 resulting in translation of the shaft directlyout of the page towards the viewer (without rotation). On the right-handof FIG. 78 roller axes of rotation G140 are perpendicular to the longaxis of the shaft G136, resulting in rotation of the shaft G136 withinthe plane of the page (without translation) when the rollers' axes ofrotation G140 are parallel to the long axis of the shaft G136, and theshaft G136 cannot be moved through the rollers G139, G140 regardless ofwhether rollers G139, G140 are turning, i.e., the shaft G136 is locked,thus this embodiment of the retractor G130 is self-retaining. At allother angles between the roller axis of rotation G140 and the long axisof the shaft G136, rotation of the rollers G139, G140 results in acombination of rotation and translation of shaft G136.

Note in FIG. 78 that varying the angle between the rollers' axes ofrotation G140 and the long axis of the shaft G136 effectively varies howthe driver roller's G139 power is spent—when the roller axis of rotationG140 is perpendicular to the long axis of the shaft G136, all of thepower of driver roller G139 is spent translating the shaft G136, andwhen the roller axis of rotation G140 is parallel to the long axis ofthe shaft G36, all of the power of driver roller G139 is spent rotatingthe shaft G136 in place. In motions in which one motion (translation orrotation) of the shaft G136 is strongly opposed and the other motion isnot, then varying the angle between the roller axes of rotation G140 andthe long axis of the shaft G136 effectively gears the roller driverG130, allowing the roller driver's axis of rotation G140 to be adjustedsuch that the power of the roller driver G139 is sufficient to generatethe desired force and motion. For example, the roller axes of rotationG140 can initially be parallel to the long axis of the shaft G136 whenthe torque source of the driver roller G139 starts rotating the driverroller G139. This causes the shaft G136 to rotate without translation.While the driver roller G139 continues rolling, the angle of the rolleraxes of rotation G140 can be continuously changed such that the shaftG136 slowly starts translating. The angle of the roller axes of rotationG140 can, thus, be adjusted to place more of the power of the driverroller G139 into translating the shaft G136. Note that controlling theangle between the rollers' axes of rotation G140 and the long axis ofthe shaft G136 can also be used to control the velocity of translationof the shaft G136.

FIG. 79 shows one embodiment that uses roller drives in a retractorG160. Retractor G160 has two opposed retraction units a first retractionunit G161 and a second retraction unit G162, each comprised of aretractor arm G168 and G170, respectively, and a retractor body G183 andG182, respectively, mounted on shaft G184. Consider first retractionunit G161: retractor body G183 houses a roller drive G171 comprised oftwo idler rollers G172 and a drive roller G175, each oriented with itsroller axis G176 of rotation oblique to the long axis of the shaft G184.The second retraction body G182 contains a set of three idler rollersG172, each oriented with its roller axis of rotation G176 oblique to thelong axis of the shaft G184. Both retraction units G161 and G162 are,thus, driven by the one drive roller G175 in the first retraction bodyG183. The angle between the rollers' axes of rotation G176 in the firstretraction body G183 and the long axis of the shaft G184 determines themotion G186 of the shaft G184 relative to the retractor body G183. Themotion G186 of the shaft G184 can be broken into its two components ofrotation G189 and translation G187 relative to first retractor body G183and rotation G190 and translation G188 relative to second retractor bodyG182. The second retraction body G182 does not drive the shaft G184;rather, the rotation of the shaft G184 drives the translation G188 ofthe second retraction body G182 and, thus, the second retraction unitG162. Engagement of the retractor arms G168 and G170 with the patient'stissues prevents rotation of the second retraction unit G162 about thelong axis of the shaft G184, so the angle between the rollers' axes ofrotation G176 in the second retraction body G182 determines thetranslation rate G188. Thus, the driver roller G175 in the firstretraction body G183 drives apart both retraction units G161 and G162with a relative velocity of G187 plus G188, thereby providing retractionG164, G165.

Note that the angle between the rollers' axes of rotation G176 and theshaft G184 in the first retraction body G183 need not match the angle inthe second retraction body G182. The angle can be such that the firstretraction body G183 generates only rotation of the shaft G184, and theangle in the second retraction body G182 can be such that the secondretraction unit G162 moves away from the first retraction unit, or anyother range of combinations. Infinitely fine and smooth control of therate of retraction by the rate of rotation of the driver roller (e.g. bya motor that actuates it) is thereby achieved by varying the anglebetween the rollers' axes of rotation G176 and the shaft G184 in thefirst retraction body G183, and also by varying the angle between therollers' axes of rotation G176 and the shaft G184 in the secondretraction body G182. A mechanism that variably changes the anglebetween the rollers' axes of rotation G176 and the shaft G184 in eitheror both retraction body G182, G183 can thus be used to control both therate of retraction and the magnitude of the thrust (retraction force).

G.4 Dovetails

Another embodiment of a retractor G190 is shown in FIG. 80. RetractorG190 uses an alternative means for providing additional degrees offreedom of motion to the retractor arms G194. The two arms G194 ofretractor G190 are mounted to the frame G192 of the retractor G190 viadovetail slides G196 and G198, the axes of which are perpendicular tothe axis of the motion of the retractor blades (i.e., the axis ofretraction). Each retractor arm G194 is thus free to slide out and back,i.e., perpendicular to the axis (or direction) of retraction. Much ofthe forgoing concerning the features and benefits of the Swing BladeRetractors G68 and G160 and applies here, except that the accommodatingmotions G200 of the retractor blades G199 enabled by the dovetails G196,G198 can be perpendicular to that of the Swing Blade Retractors G68 andG160. Additionally, the motions G200 are directly translational asopposed to rotational, as was the case for the Swing Blade RetractorsG68 and G160, and the two may be combined as desired to increase aretractor's ability to accommodate the patient's reconfiguring tissues.

FIG. 81 shows another retractor G202 that is fitted with two dovetailslides. First dovetail G204 permits motion G208 of retractor arm G214and retractor blade G216, matching the motion G200 of dovetails G196,G198 in FIG. 80. Second dovetail G206 permits motion G210 of retractorarm G214 in a direction at right angles to the first dovetail G204, withboth motions G208 and G210 being perpendicular to the axis ofretraction. This means that this retractor can accommodate both a riseand fall of the body wall and a relative sliding of the edges of theincision parallel to the incision and within the plane of the skin ofthe patient, while still delivering retraction forces to the patient'sbody wall. This design still achieves stability and force minimization(now in 2 axes) by exploiting the tendency of the patient's body wall tore-appose.

G.5 Parallelograms

In yet another embodiment of a retractor G218 shown in FIGS. 82A and82B, another mechanism is disclosed for providing an additional degreeof freedom to the retractor arms G224, G226. Retractor G218 is comprisedof two parallel dual-thrust lead screws G230 and G232 held by capturedswiveling nuts G228 in a first retraction body G220 and a secondretraction body G222. Each retraction body G220, G222 bears a retractorarm G224, G226, and a retractor blade G250, G252. Captured, swivelingnuts G228 are similar to those found in a Jorgenson clamp used forwoodwork, such as those offered by Woodworker's Supply of Albuquerque,N. Mex. These captured, swiveling nuts G228 allow movement G254 of theretractor blades G250, G252 in a direction approximately perpendicularto the axis of retraction G256 (see FIG. 82 b).

G.6 Tension Straps

Another embodiment is shown in FIG. 83, which shows a differentretractor configuration we call a “tension strap retractor” G258 thatautomatically aligns to the forces on the retractor blades G264. Tensionstraps include mechanisms integral to the strap that are capable ofgenerating the force for retraction. Here, the retractor G258 takes theform of two or more thin straps, cranial strap G262 and caudal strapG266, that wrap around, and maybe behind, a portion of the body of thepatient G260. Cranial strap G262 and caudal strap G266 are connected toretractor blades G264 which are inserted into the incision G269 to pullon the cranial rib G263 and caudal rib G265. The cranial strap G262 canbe held in position by wrapping around a portion of the patient's G260body, such as around the neck and/or shoulder. The caudal strap G266 canbe held in position by wrapping around a portion of the patient's G260body, such as around one leg. Alternatively, the straps G262 and G266might anchor on the dermis of the patient G260 or on a bedframe. In thisembodiment, retractor G258 self-aligns with the natural resistance ofthe body wall. Tension strap retractor G258 operates in tension, asopposed to a traditional compression- and bending-resisting frame. Onebenefit of a tension strap retractor G258 is that the volume of materialrequired to withstand the retraction forces in tension is a smallfraction of the volume of material required to withstand similar forcesin, say, bending. Given this, a tension strap retractor can be verylightweight, further reducing unnecessary loading of the patient'stissues.

FIGS. 84 and 85 show another embodiment of a tension strap retractorG270 adapted for sternotomy. FIG. 84 shows a front view of tension strapretractor G270, and FIG. 85 shows a cross-sectional view through apatient's body G272. Tension strap retractor G270 simply wraps aroundbehind the back of the patient G272 and automatically orients to open upan incision G275 that bisects the sternum into two halves G281 and G282.Retractor blades G278 and G280 reach into and/or around the margin ofthe incision G275, pulling back on sternum halves G281, G282. Tensionstrap retractor G270 pulls along the surface of the body of the patientG272. In this arrangement, the straps G274, G276 and G306 of the tensionstrap retractor G290 load the body wall such that straps G274, G276 andG306 remain aligned with the body wall and, thus, with the retractionforces for opening incision G275.

For tension strap retractor G270, the straps can be any thin and strongfabric, such as nylon webbing, that can resist tension. The straps candevelop tension via a pull strap with sliding buckle, a ratchet pull, awinch, or by direct shortening of the fibers of the strap (for exampleby using shape memory alloy for the fibers). To this end, the strapmight be fibrous netting surrounding pressure bladders G296, for exampleelastomer balloons residing within two-layer (or hollow) nylon webbing.In this case, the netting can be formed of fibers that run helicallyaround the strap G276, G278, and G306 as a whole. In this example, thetrajectory of the helical fibers forms an angle with respect to the pathof the main strap; the angle can be very low (10 to 30 degrees) tofacilitate developing significant force when the bladders G296 areinflated. Retraction forces can be generated by inflation alone ifdesired. Inflating the pressure bladders G296 would swell them,developing tension in the straps G276, G278, and G306, and so loadingthe retractor blades G278 and G280. The swollen bladders G296 can alsoprovide a moment enhancer G303 (i.e., a stand-off) to reduce themagnitude of the tension that must be developed to create the forcessufficient to operate the tension strap retractor G290. Alternately, thestand-off G303 function might be achieved more directly by placing pads,pillows, blocks, or other compression-resisting members between thestraps G276, Gs78, and G306 and the body of the patient G272. Saddlesand pads can be added to the straps G274, G276 and G306 to distributeloading of the straps over the patient's body G272, or to concentratethe loads in particular areas, for example those areas that canwithstand more concentrated pressure.

Another advantage of the tension strap retractor G270 is that it offersgreater access to the surgical field because it has few components nearthe surgical field and these components lay close to the body of thepatient G272 with tension strap retractor G270 having an extremely lowprofile, perhaps projecting no taller than 2 or 3 millimeters above theskin of the patient.

Tension strap retractors G290 can also be used for non-thoracic surgery.A common use of retractors, such as a Weitland retractor G312 (see FIG.86) is to pull open an incision through the skin G314 to provide accessto the anatomy beneath the skin for plastic surgery, orthopedic surgery,neurosurgery, and others. Retraction of the skin frequently requiresonly small forces, but conventional retractors in the prior art, such asa Weitland retractor G312, are typically scissor-like devices made ofsteel and are heavy, thereby interfering with surgical access andexerting unnecessary loads, especially during the second phase ofretraction.

FIG. 87 shows a tension strap retractor G320 that is small andlightweight to, for example, open the skin on an arm for vascularsurgery. The tension for retraction of the retractor blades G326 andG332 can be generated by pull tabs G324 and G334 that pull the strapG322 through a self-cinching buckle G328 and G330. Alternatively,tension could be generated by pulling the strap through a loop and thensecuring back onto the strap with Velcro.

H. Hard Tissue Engagers

Retractors, by their very nature, are typically made of rigid stainlesssteel to withstand the stresses of forcing open incision, includingincisions through rigid structures like rib cages. Rib cages arethemselves made largely of rigid bone and built to withstand thestresses of human locomotion or lifting large loads. The ribs, as ithappens, are intermingled with several much softer tissues, includingmuscles which provide actuation for breathing and modifying posture,connective tissues which transmit forces from one rib to another and tothe spinal column, vessels and arteries which supply nutrients andremove waste products, nerves providing signaling to and from the spinalchord; and all these are covered with skin and adipose tissues. During athoracotomy in which a surgeon inserts the retractor blades and thencranks to spread the patient's ribs apart, the muscles apposed to thoseribs and the nerves running along the surface of those ribs are oftendamaged when compressed between the rigid rib and the metal blades ofthe retractor. The soft tissues, supposedly protected by the ribs, areinstead caught in the middle when the retractor blades push against thebones during retraction.

In more detail, our ribs lie in a closely packed row deep under theskin, spaced about as far apart as they are wide, forming serial bonybars embedded in the muscle and other soft tissues that the ribs in turnsupport. As shown in FIG. 88A, running under the skin H42, cranial ribH46 and caudal rib H47 are roughly oval in cross section with the longaxis of the oval aligned more-or-less parallel to the surface of theskin H42. (The following description uses the terms “caudal” H45 and“cranial” H43, which refer to relative position in the body, withcranial being closer to the head and caudal being closer to the feet.)Intercostal tissues H44, which are mostly muscle and connective tissues,span the space between the cranial margin H54 of the caudal rib H47 andthe caudal margin H50 of the cranial rib H46. A delicate bundle ofnerves and arteries (the neurovascular bundle H48, which includes theintercostal nerve, lays just inside the caudal margin of each rib H46,H47.

Surgeons, aware that the neurovascular bundle 1448 can be easilydamaged, prepare to insert the retractor by slicing the interveningintercostal tissues H44 closer to the cranial margin H54 of the caudalrib H47. This lessens the probability of accidentally cutting theneurovascular bundle H48 during the incision, and it provides a pad ofmuscle on the caudal margin H50 of the rib H46 that is cranial to theincision H52, in order to protect the neurovascular bundle H48.

As shown in FIG. 88B, the retractor is inserted into the incision H52,with retractor blades H30 positioned to push against the two ribs H46and H48. Retractor blades 1430 are attached to retractor arms 1432 byfasteners H38 such that retraction pries apart the ribs H46, H47 whenretraction arms H32 separate during the first phase of retraction.

Damage to the neurovascular bundle H48, nevertheless, occurs. Asdepicted in FIGS. 89 and 90. FIG. 89 shows a cross-sectional view, andFIG. 90 shows a top view. Regions of high pressure H60 are created inthe intercostal tissues H44 that are compressed between the ribs H46,H47 and the hard retractor blades H30. The pressures are large, owing tothe large forces used to separate the ribs. Subsequently, tissues aremechanically crushed. The neurovascular bundle H48 can be pinched,especially at pinch points H82 created by the edges (i.e., corners) ofthe blades H30 where they intersect the ribs H46 and H47. The tissuepressures underlying the retractor blades H30 can be sufficiently highto block both blood flow through the vessels of neurovascular bundle H48and perfusion of all this tissue underlying the retractor blades H30.Lack of perfusion causes anoxia in theses tissues, which damages alltissues, especially nerves. Additionally, movement of ribs H46, H47during retraction can be sufficiently large that a rib H46, H47 canimpinge on the adjacent rib further from the incision, as shown in FIG.91. Again, the resulting regions of high tissue pressure H60 betweenribs can be sufficiently large that intercostal tissues H44, includingthe intercostal nerves in neurovascular bundles H48, can be damaged oneor even several ribs removed from the incision (Rogers, Henderson et al.2002).

The regions of high pressure H60 and the pinch points H82 areestablished during the first phase of retraction and are then sustainedduring the second phase of retraction for the duration of the surgicalprocedure, which can often be hours.

Damage to intercostal tissues caused by the regions of high pressure H60and by pinch points H82 is thought to underlie much of the pain causedby thoracotomies, especially damage to the intercostal nerves of theneurovascular bundles H48. Thoracotomies are considered one of the mostpainful of all surgical procedures. Pain is always intense for daysafter surgery and, unfortunately, can last for months to years, andsometimes is permanent. The long-lasting pain after a thoracotomy haslead to the identification of a “post-thoracotomy pain syndrome”.

This great pain following thoracotomies, and the associated morbidityand mortality, are the main drivers for alternatives to these open-chestprocedures, including minimally invasive surgery (MIS). While many MISprocedures have been developed, such as mini-thoracotomies, endoscopicsurgeries, and the like, their adoption rates have been low.

An improved retractor blade that decreases tissue damage duringretraction, especially to the intercostal nerve, would be of greatbenefit. It would reduce post-operative pain while retaining fullsurgical access.

To these ends, we disclose apparatus and methods for attaining favorablealignments and positive engagements with a patient's hard tissues, forexample bones (e.g. ribs) or teeth. With the various embodiments of thepresent invention one can rapidly and assuredly apply forces sufficientto displace or deform the patient's tissues for medical procedures whileentirely avoiding compressing, crushing, or compromising adjacent softtissues, thus preventing post-surgical pain.

In one embodiment shown in FIG. 92A and FIG. 92B, holes H118 are drilledfrom above into the ribs H46 and H47 and rigid posts H120 are insertedinto these holes to serve as anchors for the retractor. Holes H118 canbe drilled at an angle H119 such that, after the posts H130 areinserted, the posts possess an angle with respect to the axis of loadingto ensure the posts don't slip out of the holes during retraction. Theposts H120 can be made such that they snugly fit into the holes H118 toensure good purchase in the bone of ribs H46 and H47. Optionally, theposts H120 can possess threads and be screwed into position in the ribsH46 and H47 to ensure good purchase in the bone of ribs H46 and H47. Ajig can be used when drilling the holes to ensure appropriate angle,depth, and position of the holes H118.

As shown in FIG. 92C, the posts H120, after placement in the holes H118drilled in the ribs H46 and H47, are then used as secure anchors forretractor arms H100 that push against the posts H120 to move the ribsH46 and H47 without pushing on soft tissue. The posts H120 can be usedfor closing the incision as well.

Another embodiment is shown in FIG. 93. The posts H160 are attached bymechanical fasteners H166 to the retractor arms H170. Also, the holesH155 are drilled all the way through the ribs H46, H47. Note thatdifferent depths of the holes H155, including holes that pass throughthe ribs H46, H47, can be used with any configuration of posts H160.Note, also, that when the holes H155 are drilled all the way through theribs H46, H47, holes H155 can be used during closing, whereby suturespass through the holes H155, running from caudal rib H47 to caudal ribH46 to re-appose the ribs and to secure them into position. (It is priorart that such holes are drilled specifically for re-apposing andsecuring the ribs with sutures, but the holes are not used forretraction.)

FIGS. 94A and 94B show another embodiment of a device to engage ribs butfor which holes need not be drilled. Rather, elastic circumferentiallysurrounding clips H192 can be attached to the ribs H46, H47 such thateach rib H46, H47 is firmly clasped without exerting pressure on softtissues H44 surrounding ribs H46, H47. As shown in FIG. 94A, clip H192possesses points, or spikes, including a top spike H196 that engages theouter surface of the rib H46 and a bottom spike H194 that engages theinner surface of the rib H46. The spikes H194 and H196 automaticallyseat onto or into the surface of the bone (i.e., rib H46), crucially,away from the neurovascular bundle H48. The clip H192 is attached to adescenders H186 that are attached to retractor arm H182 by mechanicalfasteners H184. Descender H186 descends from the retractor arm H182.Clip H192 is attached to descender H186 by a flexibly bendable, tensilystiff element, such as cable or chain H188, which runs tangentiallyaround and attaches to the clip H192 at point H190. Clip H192 is hookedinto, and so loads, the ribs H180. The clip F1192 possesses a roughlyeven radius that is a function of the tension in the chain H188, thatis, the radial distance separating the clip H192 from the surface of therib H46 changes as the tension in the chain H188 changes. Use ofdescender H186 ensures an advantageous angle for pulling on the chainH188 around the circumference of the clip H192. When the spikes H194 andH196 are loaded for retraction of the rib H46, by tension on the chainH188, the resulting torque on the clip H192 acts as if to rotate theentire clip H192. But, since the clip's H192 rotation is largelyrestrained by the spikes H194 and H196 inserted onto or into the surfaceof the rib H46, the torque instead causes the clip H192 to “rise up ontiptoes,” i.e., the elastic circumferential clip H192 increases itsradius away from the surface of rib H180, doing so by angling the spikesH194 and H196 and firmly driving the spikes H194 and H196 into the boneH46, thereby more securely engaging with the rib 1446. Bottom spike H194effectively serves as a pivot point for the clip H192 which, whencombined with rotation H191 of the clip H192, forces the top spike H196into the bone H46. Thus, slippage of the clip H192 is prevented by thespikes H194 and H196, and sufficient force can be exerted on the rib H46to achieve retraction without loading the soft tissues H44, includingthe neurovascular bundle H48.

As shown in FIG. 94B, clips are placed on the both ribs H46 and H47 onboth sides of the incision H52, and retraction moves the ribs apart.

FIGS. 95A and 95B illustrate different configurations of spikes on clipsto achieve more secure engagement with the rib. FIG. 95A shows a clipH192 like those in FIGS. 94A and 94B. Clip H192 has single spikes H194,H196. Alternatively, FIG. 95B shows that a clip H256 can have multiplespikes on each end, double spikes H258 and H260 in this example, whichdistribute loading of the spikes H188 on a rib and also prevent sidewaysrolling of the clip H256 if chain H188 should pull a bit sideways.

Clips H192 and H256 are positioned after the intercostal incision ismade, and then the chains H188 are attached to the descender H186.Similarly, the chains H188, or other tensile element, can be attached tothe descender H186 with sufficient length of chain H188 to provide slackduring placement of the clip H192 or H256. After placement of the clipH192 or H256, the slack is then removed before retraction commences.Removal of the slack can be by any of several one-way slip attachments,such as a ratcheting cable tie or “zip tie” as offered for sale byNelco, Inc. of Pembroke, Mass.

FIG. 95 illustrates the placement of one or more clips to distributeloading along the ribs during retraction. Multiple single spike clipsH192 are placed on each rib H46 and H47, possibly with different numberson each rib H46 and H47. Multiple clips H192 are attached to retractorarms H182 and are, thus, spaced along the rib margin facing the incisionH52. When retractor arms H182 move apart during retraction, the multipleclips distribute loading of the rib to decrease the chance of ribfracture.

FIGS. 97A through 97D show another embodiment of a device that engagesthe ribs directly, minimizing trauma to intercostal tissues. FIG. 97Ashows a side view and FIG. 97B shows a top view. A device can cutthrough soft tissues H44 to abut hard tissues. The cut through the softtissues is a small trauma relative to the compressive loading of alarger retractor blade. Retractor arms H300 can have descender postsattached, a first descender post H304 abutting cranial rib H46 and asecond descender post H306 abutting caudal rib H47. Descender posts H304and H306 can have their positions adjusted (arrows H314 and H316) closeror farther from the centerline of the incision H52 (i.e., left-right inFIGS. 97A and 97B) to permit automatic balancing of loads as disclosedin Section F. Descender posts H304 and H306 can have sharpened edgesH310 and H312, respectively, that face the ribs H46 and H47,respectively, such that the descender posts H304 and H306 can penetratelaterally through the margin of soft intercostal tissues H44 to abut theribs H46 and H47 directly. Thus, rather than crush the intercostaltissue, descender posts H304 and H306 slice into the intercostal tissuesH44. Because descender post H302 has a vertically straight marginoriented towards the cranial rib H46, descender post H302 can abut thecranial rib H46, but does not impinge on the neurovascular bundle H48that lies just underneath the caudal edge of the cranial rib H46 (seeFIG. 97A). The sharp edges H310, H312 of descender posts H304, H306 canbe serrated, or possess other structures to engage the ribs, to preventthe descender post H304, H306 from slipping off the rib H46, H47.Alternatively, FIG. 97C shows a different descender post H334 descendingfrom retractor arm H330. Descender arm H334 has a retraction hook H336to facilitate positioning against the rib H46 and to prevent slipping.Preferably, such structures include appropriate stand-offs H338 andcurvature such as to create a hollow H340 to avoid impinging on theneurovascular bundle H48.

Descender posts can be mounted to the retractor arms such that theirpositions can be adjusted left-right (indicated by arrows H314 and H316in FIGS. 97A and 97B), variably pushing through the soft tissues H44 atthe margins H320 of the incision H52 to accommodate curvature of theribs H46, H47 and thereby ensure distribution of loads on the ribs H46,H47. Any of the embodiments disclosed in Section F are appropriate.Additionally, as shown in FIG. 97D, a retractor arm H330 can havedescender posts H350 and H352 attached by lockable, telescoping,rotatable mounts H354. Thus, after the descender posts H350 and H352have been placed into an incision, each descender post H350 or H352 canbe swung up against the rib H46, telescoped by a motion shown by arrowH356 to bring the hook H336 into contact with the bottom of the rib H46,and then locked into position.

Refer now to FIGS. 98A and 98B which show another embodiment usingretraction hooks that have an additional degree of freedom of motionfacilitating placement onto the rib. FIG. 98A shows a side view, andFIG. 98B presents a top view showing the steps of placing the retractionhook onto the rib. Consider FIG. 98A, a descender post has a shaft H366that attaches to retractor arm H364 via swivel joint H374. Shaft H366has a Retraction hook H336, including a stand-off H338, that extendsunder the rib H46 and forms a hollow H340 to avoid contact with orcompression of neurovascular bundle H48. Swivel joint H374 permitsrotation H376 of shaft H366 around an axis of rotation H375 parallel tothe axis of the shaft of the descender post H366 (as shown in FIG.983A). As shown in FIG. 98B, Step 1 (block 390), the retraction hookH336 on shaft H366 can be aligned such that, before insertion into theincision 1452, the retraction hook H336 is parallel to both the rib H46and the incision 1452. In Step 2 (block 392) of FIG. 98B, afterinsertion into the incision H52, the retraction hook H336 can be rotatedto position the retraction hook H336 under the rib H46. Additionally,the length of the shaft H366, or the distance between the retractionhook H336 and the retractor arm H364, can be adjusted (arrow H378), asshown in FIG. 98A, to further permit positioning of the retraction hookH336 relative to the rib H46.

FIG. 99 shows a three-dimensional working model of a retractor H412equipped with first and second retractor arms H414 and H416,respectively, each having three (3) descender post shafts H366 withrotatable, height-adjustable, retraction hooks H336.

FIG. 100 discloses yet another embodiment having a plurality ofdescender posts to distribute loads on a rib. Descender posts H428 canbe very thin, each not capable of displacing the rib H46, but withseveral arrayed in parallel on retractor arm H426 such that, combined,descender posts H428 can displace the rib H46. Descender posts H428 canbe, for example, stiff wires arrayed into a comb that can be placedagainst the rib H46. The descender posts H428 can be sufficiently sharpon their ends that they are placed by piercing the soft tissues H44 nextto the rib H46. The positions of the descender posts H428 can beindependently adjustable, or they can be flexible such that theyautomatically seat against the rib. As also shown in FIG. 100, the shapeof the descender posts H428 can be such that they press against the ribH46 without impinging on the space below it, thus again avoiding loadingthe neurovascular bundle residing in the soft tissues H44 there. Anynumber of hard tissue engagers can be arrayed to avoid crushing,damaging, or traumatizing any soft tissues associated with a hardtissue.

FIGS. 101A through 101E show another embodiment of a device for engaginga hard tissue, like a rib, without damaging neighboring soft tissues.Retractor arm 432 has a descender post H434 with a turn or bend H435going to a projection H436 that engages the rib H46. The projection H436is thin and pointed such that it easily penetrates the soft tissues H44adjacent to the rib H46. The projection H436 can include a tip H442 witha sharp point to engage the edge of the rib H46 such that projectionH436 of the descender post H434 firmly engages rib H46 but does nottouch the neurovascular bundle H48. As shown in FIGS. 101B through 101D,the sharp point of tip H442 can be configured such that it pierces onlythe surface of the rib H46 to prevent slipping, but can not piercefurther. For example, as depicted in FIG. 101C, the tip H442 of theprojection H436 can terminate with a spike H470 that penetrates the ribH46, but the tip of the projection itself H442 it too dull to furtherpenetrate the rib H46. As shown in FIG. 101D, the tip H442 can havemultiple spikes H472 to ensure engagement of the rib H46. As shown inFIG. 101E, projection H436 is depicted engaging the rib H46 with a spikeH470, which ensures engagement of projection H436 with rib H46 even asrib H46 moves (shown by arrow H488).

FIG. 102 shows a section view of a thoracotomy performed by anotherembodiment in which the rib is firmly grasped on both sides to permitdeterministic control of its motion, i.e. the position and orientationof the rib is always controlled. Retractor arms H500 each have a spacerbar H506 to which are attached paired descender posts H502 and H504. Thepaired descender posts H502 and H504 engage both sides of the ribs (forexample, H46). The directions of retraction (i.e., rib spreading) areshown by arrows. Both descender posts H502 and H504 are straight andengage the ribs H46 laterally. The sides of the descender posts H502 andH504 can have serrations H503 where they engage the ribs to reduceslipping of the descender posts H502 and H504 on the ribs H46. Thedistance H491 separating the paired descender posts H504 and H502 can beadjustable to permit positioning the paired descender posts H502 andH504 firmly against the margins of rib H46 thereby accommodatingvariations in cranial-caudal width of rib H46. This embodiment allows aretractor to firmly grasp the rib H46, permitting deterministic controlof rib position throughout retraction.

Referring now to FIG. 103, a retractor H510 can also engage ribs H519and H525 further from the incision H526, in addition to the ribs H521and H523 adjacent to the incision. As shown in FIG. 103, a retractorH510 can possess a plurality of retractor arms (H528, H530, H532 andH534), each equipped with descender posts (H529, H531, H533 and H535,respectively). The retractor arms H528, H530, H532 and H534 can havecoordinated motion, with respect to one another, that includes differentspeeds such that the retractor arms H528, H530, H532 and H534 eacheffect a different displacement over the same time. For example,retractor arms 1 (H528) and 2 (H530) form a pair on one side (thecranial side, H537) of the incision H526, and both retractor arms 1(H528) and retractor arms 2 (H530) can move in the same direction ofretraction (H536), but the displacement (H511) of retractor arm 1 H528can be less than the displacement (H513) for retractor arm 2 H530 (e.g.,retractor arm 1 can move more slowly than retractor arm 2). (Retractorarms 3 H532 and 4 H534 can, similarly, form a pair on the opposite, orcaudal H539, side of the incision H526.) This varying displacement ofthe retractor arms reduces the pressure in intercostal space A H520 andintercostal space B H522 (and their respective neurovascular bundles,grouped H524) arising from ribs H518, H519 and H521 (cranially) andH523, H25 and H527 (caudally) impinging on one another duringretraction.

FIGS. 104A, 104E and 104C show another embodiment in which anarticulating clip is used to grasp a rib without compressing neighboringsoft tissues. FIGS. 104A through 104C show an action sequence of anarticulated clip H553 meeting, closing, and locking down onto a rib H46.In the sequence, a descender post H544 is fitted with a moveable, deeplycurved, articulated clip H553 having a top half jaw H554 and a bottomhalf jaw H555 attached by a pivot H546 to the descender post H544. Eachhalf H554 and H555 possesses a sharp point H562 and H560, respectively,for engaging the rib H46, and a tab (one tab, H556, projects up and isassociated with the bottom clip half H555, and another tab, H558,projects down and is associated with the top clip half, H554. The cliphalves H554 and H555 can be spring-loaded such that they stay open (withjaws spread wide) before loading (i.e., before contacting the rib H46).The clip half tabs H556 and H558 are cams shaped so as to generate atorque when the descender post H544 with all associated components ispushed against the rib H46. When the rib H46 impinges on the clip halftabs H556 and H558, each tab is pushed apart and away from the other,causing each half of the clip H554 and H555 to rotate in the oppositedirection (i.e., the top half clip H554 comes down and the bottom halfclip H555 comes up), thus using the force applied by the rib H46 tobring the sharp points H560 and H562 into position against the rib H46to forcefully secure it. The shapes of tabs H556 and H558 cooperate withthat of the clip jaw halves H554 and H555 such that a space is createdprotecting the neurovascular bundle H48 from any contact whileretraction proceeds. The sharp points H560 and H562 are configured suchthat they penetrate only the surface of the rib H46, far behind theneurovascular bundle H48 as the descender post H544 is pushed morefirmly against the rib H46. Thus, further force (or travel) of thedescender post H544 against the rib H46 is born by the sharp points H560and H562 loaded into hard, resistant bone, and not just the tabs H556and H558, thereby limiting any pressure exerted by the tabs against thesoft tissues adjacent to the rib H46 and, thus, protecting theneurovascular bundle H48.

J. Compensating for Retractor Deformation

Many biological tissues are very rigid. For example, rib cages are madeof rigid bone connected by numerous ligaments, muscles, andtendons—strong enough to withstand the stresses of human locomotion orlifting large loads. Thus, the forces required to deform these tissuesduring procedures such as sternotomy or thoracotomy are significant. Wehave measured forces of up to 500 N during thoracotomies and 250 Nduring sternotomies on pigs weighing 50 to 60 kg. Forces on vertebraldistractors are also large.

Retractors, by their very nature, are typically made of rigid stainlesssteel to withstand the stresses of forcing open rib cages. However,retractors deform under load. Deformation of a typical Finochietto-styleretractor (e.g. a Finochietto, see FIG. 2, Burford, Ankeney, or otherthoracic retractor) is primarily of two types—the arms bend and twist.Deformation of the retractor is more complex, e.g. including bending ofthe rack of the rack and pinion.

FIG. 105A shows the bending of the retractor arms J6, J10 of aFinochietto-style retractor J2 in the prior art when loaded duringretraction. Retractor J2 has two retractor arms J6 and J10. Retractorarm J6 is fixed to the rack J8 of a rack-and-pinion drive J4 that isdriven by a manual handle J5. Each retractor arm J6 and J10 has anattached retractor blade J12 and J14, respectively, that engages thepatient's tissues during retraction. Bending J20 of the retractor armsJ6 and J10 causes the distance J36 between the retractor blades J12, J14to decrease, whereas the distance J38 between the retractor arms J6, J10is not greatly effected.

FIG. 105B shows twisting of the retractor arms J6, J10 of aFinochietto-style retractor J2 in the prior art when loaded duringretraction. Retractor blades J12 and J14 push against ribs J30 and J32,respectively. The force on the retractor blades J12, J14 twists theretractor arms J6, J10, causing the distance J36 to decrease.

We have measured deformations, decreases of J36, of up to 2 cm when theretractor blades J12, J14 are first separated 10 cm and then loaded with500 N; in other words, the retractor blades J12, J14 are forced together20% of the separation J36 when loaded with forces seen in thoracotomies.

These deformations of the retractor J2 are elastic; the retractorJ2deforms like a spring under load. If the load decreases, the deformationof the retractor J2 decreases, and the retractor blades J12, J14 movefurther apart.

The tissues against which the retractor applies this load areviscoelastic. Unlike an elastic material, a viscoelastic material willcontinue to deform when loaded, even if the load is constant—it willexhibit creep.

This combination of an elastically deformed retractor J2 pushing againsta viscoelastic material creates a problem. Consider a sternotomy, asurgeon retracts (first phase of retraction) to a desired opening of theincision and then stops (second phase of retraction), striving not toretract wider than necessary to reduce damage to the tissues of thechest. Many retractors are self-locking or have a lock mechanismdesigned to hold the incision at that desired opening during the secondphase of retraction. However, the retractor J2 has deformed during thefirst phase of retraction, and now the elastic deformation of theretractor J2 continues to push against the viscoelastic materials of thechest during the second phase of retraction, causing the thoracicopening to further widen as the viscoelastic materials of the chest wallcreep under the elastic force of the retractor. This results in anunnecessarily wide thoracic opening, increasing damage to the tissues ofthe chest wall. For example, cardiothoracic surgeons report that theywill hear a “pop” or “snap” as a rib breaks, sometimes minutes aftercessation of the first phase of retraction.

This problem is encountered whenever any surgical instrument or medicaldevice is used to deform a biological tissue because biological tissuesare viscoelastic. Examples include, but are not limited to, retractionof skin for access to subdermal tissues, distraction of vertebrae forsurgeries on intervertebral discs or to manipulate vertebrae for fusionor for other fixation, separation of joints for surgery on cartilage orfor joint replacement, forcing open an annulus or tube with aninflatable device, such as angioplasty, or any other procedure requiringdeformation of a biological tissue.

We disclose apparatus and methods for deforming a patient's tissues tothe degree defined by the physician, reducing any further deformation ofthe tissue after the desired deformation is attained, and, thereby,reducing the chances of unnecessary tissue trauma.

One solution to this problem is to make the retractor exceedingly rigidthrough the use of materials having large Young's modulus (e.g.,titanium which is expensive) or by the use of members having largecross-sectional area (e.g., wide, thick members which adds weight to theretractor). This retractor will still deform elastically, but theelastic deformation of the retractor will be small, so it will imposeonly a short distance of creep on the tissues of the chest.

An alternative solution is a thoracic retractor that deforms elasticallybut the surgical opening is controlled by a servo-mechanism thatmaintains the opening at the point set by the surgeon. Thus, as thetissue begins to creep, causing the retractor blades to move apartelastically, the servo-mechanism causes the retractor to close slightly,thereby decreasing the elastic deformation of the retractor and applyingonly the force required to maintain the surgical opening at the pointset by the surgeon.

FIG. 106 shows one embodiment in which the servo-mechanism controls thedistance J36 between the retractor blades J12, J14 of a retractor J40.The servo-mechanism is comprised of a motor J44 that opens the retractorJ40, a distance measuring device J41 that measures the surgical opening(e.g. a linear potentiometer), and a servo-controller J46 that receivesthe signal from the distance measuring device J41 and then adjusts theposition of motor J44 to maintain the desired surgical opening, even asthe tissue creeps. Any actuator that effects the deformation of thetissue (i.e. that powers the first phase of the retraction) can be used;thus, for the embodiment shown in FIG. 106, the actuator that opens theretractor J40 is also the actuator controlled by the servo-controllerJ44.

An alternative to direct measurement of the surgical opening forservo-control, as shown in FIG. 106, is to use the force-deformationrelationship of the retractor (e.g. a spring constant or aforce-deformation curve). During use of the retractor, the force on theretractor is measured with a force measuring device, and then thedeformation of the retractor is determined from the measured force usingthe force-deformation relationship. This has the advantage that nomeasuring device is present in or near the surgical opening.

FIG. 107 presents an algorithm J50 illustrating one way to implement aservo-mechanism that uses force measurement with a force-deformationrelationship. A surgeon retracts to a desired opening (block J51) andthen activates the servo-mechanism (block J52). The position of themotor is recorded by the servo-mechanism (block J52), the force on theretractor is measured (block J52), and the motor begins to hold position(block J54). Force is then measured continuously (block J56). If forceremains constant, then the motor continues to hold position (decision atblock J57 then to step J58). If force decreases (due to creep of thebiological tissue) (block J57 then to step J59), then a translator (e.g.an electrical circuit, possibly including a microprocessor) uses theforce-deformation relationship to convert the change in force on theretractor into a change in deformation of the retractor (block J60). Thetranslator then instructs the motor to move to correct for the change indeformation, thereby keeping the surgical opening at the separation setby the surgeon (block J62) returning the feedback loop to block J54.

A similar algorithm can be used to correct for deformation throughoutretraction. Thus, rather than correct for changes in deformation onentering the second phase of retraction, the algorithm can correct fordeformation throughout both the first and second phases of retraction.With such an algorithm, the separation achieved by the retractor blades(i.e., distance J36) will then match the separation seen by the surgeonwhen looking at the retractor arms (i.e., distance J38). This algorithmalso can be part of an automated retraction system to ensure thatseparations J36 intended by the automatic retraction system are, infact, the separations achieved.

FIG. 108 shows a retractor J70 that can control the distance J36 betweenthe retractor blades J73, J77 by using servo-loop J78 that implements analgorithm such as algorithm J50. The retractor has a first retractor armJ72 and a second retractor arm J76 that is driven relative to the firstretractor arm J72 by a motorized rack-and-pinion drive J78 comprised ofa rack J74 attached to the first retractor arm J72 and a drive housingJ80 attached to the second retractor arm J76. Retractor arms J72 and J76have retractor blades J73 and J77, respectively. The drive housing J80houses a servo-motor J84 and a servo-controller J86 that controls theservo-motor J84. The surgeon opens the retractor J70 by providinginstructions to the servo-controller J86, for example with a rotatingknob J88 that replaces the crank of a manual rack-and-pinion. A forcemeasuring device J90, for example a strain gauge, is placed on thesecond retractor arm J76 to measure force on the retractor J70. Atranslator J82 in the drive housing J80 receives signals from the forcemeasuring device J90 and implements the algorithm J50. Placement of theforce measuring device and the translator can be at any of severallocations, such as on the fixed retractor arm, but placement of allthree components—servo-motor, translator, and force measuring device, onthe moveable retractor arm simplifies the design.

FIG. 109 shows another retractor J100 that uses two actuators, a firstactuator J101 to drive the first phase of retraction and a secondactuator J108 to adjust for changes in deformation arising from creep inthe tissues during the second phase of retraction. During the firstphase of retraction the first actuator J101, a hand-crankedrack-and-pinion in this example, is used to by the surgeon. A secondactuator J108 attached to one arm of the retractor J100, for example thefirst arm of the retractor J6, is controlled by a servo-mechanism J110and is used to correct for changes in the deformation of the retractorJ100 due to creep of the tissue during the second phase of retraction. Aforce measuring device J102, for example a strain gauge, measures forceon the first retractor arm J6. A translator J104 detects changes inforce, translates these to changes in the deformation of the retractorJ100, and signals the servo-controller J106 to instruct the secondactuator J108 to move and thereby remove the change in the surgicalopening resulting from the change in the deformation of the retractorJ100. The second actuator J108 can be a servo-motor, a voice coil, ahydraulic cylinder from which fluid is released to move the retractorblade J12, or any other actuator that can move the retractor blade J12such that the retractor blade J12 moves closer to the opposing retractorblade J14 when a decrease in force on the retractor is detected by thetranslator. Such a device as shown in FIG. 109 can either be integratedinto a retractor or be a component that attaches to an existingretractor.

K. A Thoracic Retractor Combining Elements of the Earlier Sections

FIGS. 110 through 114 present a thoracic retractor K2 used forthoracotomies. This thoracic retractor K2 combines components disclosedin earlier sections. Thoracic retractor K2 comprises two opposingretractor arms K4 and K6 attached to retraction driver K60.

FIG. 111 shows retraction driver K60. Retraction driver K60 comprises amotor-driven rack-and-pinion, with the pinion driven by a servo-motorK40 controlled by servo-controller K42 and powered by battery K44.Processor K46 receives input from strain gauge sensors K14 and K18 thatmeasure the forces on the retractor arms K6 and K4, respectively. Straingauge sensors K14 and K18 can be single gauges or multiple gaugeslocated in multiple locations and arrayed in, for example, a full bridgeconfiguration; additionally, strain gauge sensors K14 and K18 can bemounted where the strains in the underlying material are expected ordesigned to be large to increase the sensitivity of force measurement.Processor K46 is in communication with servo-controller K42 forautomatic control of the servo-motor K40. Retractor arm K4 attaches tothe rack K8 connector K5 via and then rotatable mount K16. Retractor armK6 attaches to driver housing K10 via connector K7. The attachment ofretractor arms K4 and K6 to connectors K5 and K7, respectively, issecured with fasteners K12. Examples of fasteners include screws, clips,or any other appropriate mechanical fastener.

FIG. 112 shows retractor arm assembly K50 that attaches via retractorarm K4 to connector K5 to rotatable mount K16. A similar retractor armassembly is attached via retractor arm K6 to driver housing K10.Retractor arm assembly K50 comprises retractor arm K4 which attaches tobalance arm K20 via rotating mount K24; two daughter balance arms K26which attach to balance arm K20 via rotating mounts K30; and twodescender posts K52 each with hook K54 attaching to each daughterbalance arm K26 via rotatable mount K34. Thus there are four descenderposts K52 each with hook K54. Each descender post K52 is attached to thedaughter balance arm K26 by rotatable mount K36 such that hook K54rotates as shown in K56. Rotatable mount K36 can include a heavy sleeveK34 that reinforces the joint.

FIG. 113 shows an enlarged view of rotatable mount K16 which providesretractor arm assembly K50 an additional degree of rotational freedom,as disclosed in Section G. Rotatable mount K16 comprises rod K62 that isrigidly coupled to rack K8. Sleeve K64 is attached to rod K62 andsecured by an E-clip (not shown). Rotatable mount K16, therefore,provides for rotation K66 of retractor arm assembly K50.

FIG. 114 shows the shapes and sequence of attachment of retractor arm K4to balance arm K20 and daughter balance arms K26 for retractor armassembly K50. Rotatable mounts K24 and K30 can be made by connectorpins; alternatively, rotatable bushings or bearings can be used.Rotatable mounts K24 and K30 can be made loose to provide some freedomof alignment out of the plane of the page of FIG. 114.

Connectors K5 and K7 can be replaced by appropriate snap-togetherfittings permitting the retractor arms K4 and K6 to be easily attachedand removed. Furthermore, connectors K5 and K7 can include electricalconnectors for transmission of power or electrical signals to electricalcomponents on or connected to the retractor arms K4 and K6 or todifferent retractor arm assemblies K50. Such electrical components caninclude sensors, processors, motors or other actuators, data inputinterfaces, data or status indicators, or other advantageous electricalcomponents.

Retractor assembly K50 is designed to distribute the forces along a ribduring a thoracotomy. Other retractor assemblies designed for otherprocedures, such as a sternotomy, can be attached to rack K8 and toretraction driver K60, optionally with rotating mount K16 a replaced bya rigid connection or other moveable mount.

Retractor arm assembly K50 can be a disposable component. Retractor armassembly can include the battery K44, and if K50 is a disposablecomponent, this would permit the attachment of a fresh battery for everyuse.

Instructions to the servo-controller K42 and processor K46 can be via auser interface that is integral to retraction driver K60. An example ofa user interface is shown in FIG. 115. The interface can include a panelin which membrane buttons activate functions such as start retractionK72, pause retraction K74, fast forward or accelerate retraction K76,emergency open K78, rewind or reverse retraction K80, fully close theretractor K82, set duration for retraction K84, set distance ofretraction K86, and a display K80 for showing information to the user,for example retraction progress with a progress bar, force on theretractor, or other information.

The thoracic retractor K2 shown in FIG. 110 has been constructed todemonstrate selected embodiments described above and, specifically, todemonstrate functioning of the self-balancing retractor arms asdescribed in Section F (e.g., see FIG. 55), the rotating retraction armand retraction assembly as described in Section G (e.g. see FIG. 74),hook-shaped tissue engagers as described in Section H (e.g. FIG. 98),and automated retraction with detection of trauma as described inSection C (e.g. algorithm C300 in FIG. 42). Motor K40 is a model EC2250W from Maxon Precision Motor Inc. The prototype does not have batteryK44 or servo-controller K42 or processor K46 housed in driver housingK10. Rather, these functions are provided by an off-board power supply(16V, 4.5A), servo-controller (EPOS 24/5 motor controller from MaxonPrecision Motor, Inc), and computer connected by a cable. Strain gaugesfrom Vishay Micro-Measurements, Inc. are placed at locations K14 andK18, arranged as full bridges, to measure forces on arms K6 and K4,respectively. Power to and signals from these strain gauges is providedby signal conditioners (Model OM-2-115 from 1-800 LoadCell), which thensend signals to a data acquisition card (Model USB-6211 from NationalInstruments, Inc.) attached to a laptop computer. Custom software formotor control and data acquisition is written in LabVIEW from NationalInstruments, Inc.

FIGS. 116A and 116B show retractions from two thoracotomies. These arefully automated retractions. The surgeon placed the retractor into theincision, rotated the hooks K54 on the descender posts K52 under theribs, and then a remote operator initiated computer-controlledretraction—the computer controlled the rest of the retraction. Theretraction trajectory was programmed to be parabolic (distance as afunction of time, retraction speed initially higher, continuouslydecreasing throughout retraction, and approaching zero speed as fullretraction is approached). The algorithm C300 described in FIG. 42 wasused to automatically pause the retractor, thereby acting as a detectorand automatic response to imminent tissue trauma. If a pause wastriggered, then after the pause, the computer calculated a new parabolictrajectory starting at the current position and reaching the desired endpoint; for example, consider the retraction in FIG. 116B:

-   -   the desired endpoint was 62 mm;    -   retraction was to occur over 45 seconds;    -   a pause occurred at 43 mm after 20 seconds had elapsed, with the        pause being 20 seconds long; thus    -   the remaining retraction distance (62−43=19 mm) was to be        covered in (45−20−20)=5 seconds.

Alternate algorithms for desired endpoints, desired retraction duration,pause durations, and means of recalculating the trajectory after thepause can be used. Alternate algorithms could be:

-   -   Desired endpoint=50 mm; desired retraction duration=50 s; pause        duration=15 s; if pause occurs in last 30 s of retraction, then        set the pause duration to be equal to half the remaining time;        or    -   Desired endpoint=100 mm; desired retraction duration=2 minutes        (120 seconds); pause duration=one-third of time remaining at the        initiation of a pause.        The complexity of the algorithm is limited only by such things        as the processing power of the processor K46, the numbers and        types of sensors used, etc.

FIG. 116A shows the displacement K100 and forces on the right arm K102and left arm K104 for a retraction to 50 mm over about 35 seconds. Thisretraction should be compared to a similar retraction performed with aninstrumented Finochietto retractor (shown in FIG. 37) for retraction to52 mm over about 50 seconds. Both retractions in FIGS. 37 and 116A wereperformed on the same animal. The retraction in FIG. 37 was at rib pair4/5 on the left side, and the retraction in FIG. 116A was at rib pair4/5 on the right side. Returning to FIG. 116A, retraction starts K106 at2 seconds and follows a substantially parabolic trajectory, withretraction ending at K108. We have found that such substantiallyparabolic trajectories have less evidence of tissue trauma than othertrajectories, such as linear trajectories or, as in FIG. 37, steppedtrajectories. It is important to note several things:

-   -   (1) No pause was triggered.    -   (2) The maximum force generated during retraction was about 300        N, about 25% less than the 400 N observed with the instrumented        Finochietto during retraction to 52 mm over 50 seconds (FIG.        37). This lower force of retraction is especially noteworthy        because the more rapid retraction in FIG. 116A should have        required more force than the slower retraction in FIG. 37.    -   (3) The forces on the two retractor arms are nearly equal,        unlike the unequal forces seen on the retractor arms in FIG. 37.    -   (4) The force traces K102 and K104 in FIG. 116A are exceedingly        smooth, unlike the extremely jagged traces seen in FIG. 37. Note        that all the data presented in FIGS. 116 and 117 are raw        data—the data are not smoothed, the traces are not fitted        curves.

FIG. 116B shows another retraction with retractor K2. This retractionwas at rib pair 5/6, right hand side, of the same animal as in FIGS. 37and 116A. We performed multiple retractions on this rib pair, going toincreasingly wider endpoints, in an attempt to get a pause to beinitiated by the algorithm C300. FIG. 116B shows the third retractionwhich was to an endpoint of 62 mm over 45 seconds. Retraction started atK110 and ended at K111. A pause K112 was triggered by a negative-goingspike (too small to see in this figure) at the point marked by the arrowK113 approximately 20 seconds after starting retraction. Retractionbefore the pause produced a very smooth displacement trace K114 andforce traces (right and left arms collectively labeled K118). Only asmall amount of force relaxation is evident in the pause. The retractionafter the pause was very rapid, due to the short time allowed by thealgorithm (about 5 seconds), but again produced a very smoothdisplacement trace K116 and force traces, right and left armscollectively numbered as K120.

It is noteworthy that the forces on the retractor relaxed only slightlyduring the pause in FIG. 116B and also at the end of the retractions inboth FIGS. 116A and 116B, relative to the relaxation seen after each½-rotation of the crank in FIG. 37. This indicates that slow, steadypulling permits force relaxation to occur simultaneously with retractionand, therefore, also indicates that there is an optimum retraction speedthat maximizes force relaxation and thereby reduces forces duringretraction. A substantially parabolic trajectory, as described above,provides such an optimal retraction.

FIGS. 117A, 117B, and 117C present the same data from the retractionsshown in FIGS. 116A and 116B, but show only force for the left retractorarm; these figures also show the second derivative of the force,d²F/dt², referred to here as the Fracture Predicting Signal, FPS, wherefracture can be of any tissue (e.g. rib, ligament, tendon, muscle)giving rise to tissue trauma.

FIG. 117A shows the retraction from FIG. 116A. Traces for both the FPSK130 and force K104 on the left retractor arm are presented. The FPStrace K130 is constant, with low noise, at zero throughout theretraction. There are no negative-going spikes and no increase invariance of the signal that would trigger a pause, so there was no pausein this retraction.

FIG. 117B shows the retraction from FIG. 116B. The force trace K132 ispresented from the left retractor arm only. Here, there is a prominentevent K134 at about 24 seconds that triggers the pause K112.

FIG. 117C shows the event K134 with an expanded scale. A small drop inthe force K132 occurs in event K134, a decrease of only about 3N (˜1% ofthe maximum retraction force during this retraction). This creates anegative going spike K136 in the FPS K130 that triggers the pause.Retraction stopped 0.2 seconds after the drop in force K132(displacement trace not shown).

Returning to FIG. 117B, there is another event K140 in the FPS duringretraction after the pause. This event was not sufficient to trigger asecond pause, and retraction proceeded to completion K111.

L. Tissue Engagers: “Safe Tissue Retraction Elements for Thoracotomy”Introduction to the Problem Tissue Engagers (Safe Tissue RetractionElements) for Thoracotomy Introduction to the Problem

Every 15 seconds, a thoracic surgeon enters a patient's chest byspreading the space between two adjacent ribs. After choosing a locationand slicing through the patient's intercostal musculature, the surgeonfirst (1) inserts the retractor's blades into the incision, then (2)ensures the retractor blades are parallel to and apposed to theincision's margins so that the blades will open along an axis (theretraction axis) lying perpendicular to the line of the incision, and(3) forcefully cranks open the retractor to widen the intercostal space.

Unfortunately, the design of thoracic retractors hasn't changed much in75 years. Tissue trauma is common, including broken ribs, crushed nervesand vessels, and torn muscles, ligaments and cartilage. Knowing this,many surgeons preemptively cut nerves or remove rib sections in anattempt to confine the damage. Clearly there is a need for improvementsto thoracic retractor design.

Issues With Current Thoracic Retractor Blade Designs

Today's thoracic retractors employ stiff retractor blades stamped out ofstainless steel plate, usually rectangular and possessing fenestrationsthrough the plate. They are minimally finished; in fact, the blades'corners are intentionally left sharp to bite into the exposed muscletissue to prevent slippage under load. Further, the retractor bladespossess wide, right-angled shelves at their tips (also with sharpcorners), the better to catch hold of the incision's margins, to preventthe retractor blades' rising up and out of the incision as the ribs arespread open. With the retractor blades cranked together, closed forinsertion, these shelves are much wider than the initial gap created bythe incision through the intercostals. To insert the blades the surgeonmust therefore force the wide edges of the shelves past the patient'sfreshly cut muscle, jamming that muscle against the patient's ribs. Onceinserted, these retractor blades continue to damage tissues, forexample, when the retractor blades are settled in place, sharp edges areadjacent to the fragile, respiring lungs. The aforementioned tissuetrauma of then spreading the ribs leads to severe pain, prolonging thepatient's recovery and trading quality of life for quantity. Theresulting healthcare costs are unnecessarily high. Is this avoidable?

Solution

Physcient here discloses novel devices and methods in the field ofTissue Retraction Elements (TRE) enabling and improving the process of:

-   -   (1) Inserting a retractor's Tissue Retraction Elements into a        thoracoscopic incision,    -   (2) Orienting and Settling those Tissue Retraction Elements into        place against the margins of the thoracoscopic incision to be        retracted, and    -   (3) Applying Force against those margins to expose the chest        cavity.

We propose a device that is easy to insert without damaging thepatient's tissues, that gently and securely self-orients and engages thetissues forming the margins of the patient's incision, and that safelyapplies force throughout the retraction process. Further, the improvedTissue Retraction Elements are also easier for the surgeon to use, areeasier to remove, are self-adjusting and improve overall patientrecovery. Surgeon, Patient and Hospital all benefit.

Inserting the Tissue Retraction Elements Without Trauma

Physcient discloses here multiple devices and methods for insertingretraction elements of a thoracic retractor. The portion of the thoracicretractor that is to be inserted into the patient's chest cavity(hereinafter referred to as the Tissue Retraction Elements, or TRE) canpossess certain attributes to prevent tissue trauma from insertion:

First, the TRE can be thin in profile (“profile” here defined as theplane view of the incision in section, see FIG. 118 and FIG. 119), so asnot to spread or stretch the ribs apart as the device is insertedparallel to the incision. The TRE might also be thin enough in profileto avoid any contact with the freshly exposed margin of the patient'sincision (FIG. 118).

Second, the TRE can possess an overall, grossly rounded shape, free ofany corners, rectilinear portions, or other substantial protrusions thatcould catch hold of, impinge on, slice, cut, dig into, pierce, hookinto, grab or otherwise injure tissues on the way in, i.e., during theinsertion step (FIG. 119).

Third, the surface or surfaces of the TRE can be free of fineprojections, surface imperfections, edges, mold lines, or textures; theTRE can be polished smooth, for example as shiny and smooth as glass, tomore easily slide easily into place without friction or impediment (FIG.116C).

Fourth, the TRE can be constructed all or in part of a very low frictionmaterial, so as to minimize shearing of the exposed margins of theincision should any contact occur during insertion (FIG. 116D).

Fifth, the TRE can be lubricated, to reduce friction between the TRE andthe patient's tissues even further (FIG. 116E-G). Any number oflubricants could be used, including FDA-cleared lubricants. Thelubricants could be applied to the surface of the TRE during theprocedure or before (for example during factory-packaging the TRE in asterile bag) (FIG. 116E), or the device could be designed so thatlubricants emerge from the TRE (FIG. 116F). Further, the TRE could becoated or made with a substance that, when contacting the wet surfacesof the freshly exposed margins of the patient's incision, creates therea lubricant or lubricating effect (FIG. 116G). For example, the TRE canincorporate a hydrogel that takes up water and becomes slippery.

Sixth, the TRE can move, flex, bend, or otherwise behave in a compliantmanner (FIGS. 116H-I). Since the patient's tissues are diverse andinclude some highly flexible, compliant tissues, the TRE can itself beconstructed all or in part of an elastomer, rubber or other soft,compliant material, so as to give way upon contact with the patient'stissues (FIG. 116H). The Young's modulus of the compliant material canbe substantially similar to one or more of the patient's tissues. Forexample, the modulus of the TRE could be close to the modulus of thefreshly exposed muscle, to match the muscle's shearing behavior,preventing steep shear gradients there. The modulus of the TRE (or aportion thereof) might also be made lower than, or greater than, theexposed tissues so as to give way, or push and guide, as is deemedappropriate. Any number of FDA-cleared polymers might be used, includingplasticizers for varying their modulus. Alternatively, the TRE mightinclude a substantially rigid component(s) working in concert with acompliant component(s) (FIG. 116I), for example associated with joints.Further, the compliant component might not be in direct contact with thepatient's tissue.

Seventh, a TRE could be capable of changing shape. While a thin orflattened profile permits easy entry into the patient's incision, a TREdesigned solely for easy entry might not be optimal for engaging norholding the patient's tissues under load. The TRE can be designed to becapable of changing shape from a first, thin profile favoring easyinsertion to another, subsequent, second profile favoring securelyretracting the patient's tissues. The shape change can be achieved anynumber of ways. We'll describe at least two here.

Articulated Joints—Finger

One embodiment (FIGS. 121-126C) of a shape-changing Tissue RetractionElement is an Articulated Safety Finger (ASF). The ASF mimics thestructure of the surgeon's own fingers (FIG. 121), which were likely thefirst “retractors” employed. The ASF can be constructed withsubstantially rigid, jointed segments (i.e., “bones”) held together by acompliant sheath (i.e., a “skin”) and actuated by a cable (i.e.,“tendon”) (FIG. 122). The cable can be very stiff in tension, or it maybe designed to be somewhat compliant to permit some accommodation of theload of the patient's tissues on the Articulated Safety Finger.

The ASF starts out straight, for insertion (FIG. 123). Once inserted,the tendon can pull on the segments (FIG. 124A) to flex them until thetip of the Articulated Safety Finger rests against the inside of thepatient's rib (FIG. 124B). FIG. 125 shows an embodiment of theArticulated Safety Finger ready for retraction.

The ASF's cable (i.e., tendon) could be designed to automatically pulland flex the ASF as a part of the insertion or retraction process, orthe action of the cable could be under the manual control of the surgeon(FIG. 126A-C, showing a surgeon pushing the Finger Flexing Lever). Seealso FIG. 127 for a more detailed drawing of the parts of the ASF'sFinger Flexing Handle (aka Finger Flexing Lever). See FIG. 128 for adepiction of one way the Finger Flexing Handle (Lever) can drive thecable motion.

The flexing action and proportions of the ASF can be designed toautomatically create a gap that avoids applying any force to theneurovascular bundle (refer again to FIG. 122).

Further, Settling the Tissue Retraction Elements into Place WithoutTrauma

Swinging Safety Fingers

Another embodiment (FIGS. 129-130B) of a shape-changing TissueRetraction Element is a Swinging Safety Finger (SSF) (oblique view, FIG.129). Designed without any sharp surfaces or projections, the SSF startsout folded flat in profile for easy insertion (FIG. 130A). One advantageof the SSF is that the surface area of the tissue retraction elementsthat are projecting down into the incision can be designed to make theSSF TRE respond to initial loading (e.g., near the beginning of the ribretraction process) by automatically reorienting the SSF TRE to presenta new profile shape designed to safely engage and capture the tissues asa part of the retraction process (FIG. 130B). This reorientation canoccur within the space of the incision and can involve SSF TRE rotationabout one or more axes. This rotation can be passive, driven by ribretraction, or it can be actively controlled.

One way for the SSF TRE to accomplish automatic, passive reorientationis (1) to arrange an axis (about which a SSF TRE might swing, called aswing axis) oriented and projecting substantially up and out of thechest cavity, and (2) arranging a substantial majority of the area ofthe tissue retraction element to be located both within the depth of theincision (and so impinging upon the surface of the margin of theincision) and located some distance to one side of a line drawn from theswing axis perpendicular to the retraction axis (FIG. 131). The portionof the SSF TRE that contains the actual joint about which the SSF TREswings can be located up out of the incision (for example, above theskin). Looking down into the incision, the deep, off-center portion ofthe SSF TRE thus forms a moment arm with its fulcrum at the swing axis.

Refer to the deployment sequence in FIGS. 132A-C. Before beginning ribretraction, the SSF TRE is oriented flat and parallel to the line of theincision for easy insertion (FIG. 132A). As the rib retraction processstarts (FIG. 132B), the high, joint section passes freely and easilyacross the patient's skin, perpendicularly away from the incision andparallel to the retraction axis. At the same time, however, the marginof the incision resists passage of the deeper, flat area of the SSF TRE.Given the moment created by the off-center portion of the SSF TRE, theresistance of the tissue causes the entire TRE to swing backwards aboutthe swing joint as retraction proceeds. The SSF TRE will swing throughwhatever angle that that design permits. If the motion about the SSF TREjoint is unrestricted, the force of the oncoming chest wall tissuesmeans that the whole SSF TRE will naturally swing through an angle ofaround 90 degrees, until the deep portion of the SSF TRE trails directlybehind the SSF TRE joint (FIG. 132C), pointing back at the incision.Note that the amount of SSF TRE rotation can be limited to any arbitraryangle by providing limit stops in the swing joint, by providingprogressive resistance of a compliant element associated with the SSFTRE, by providing a SSF shape that reaches torque equilibrium with thepatient's tissues at a chosen angle, or any other rotation ortorque-limiting means.

The shape of the deep portion of the SSF can be so designed so that asit reorients as it swings about the swing joint, it presents theimpinging chest wall tissues with a profile that changes over time(FIGS. 133A-F). During initial retraction, such a changing profile canautomatically guide the relative positions of the SSF TRE and thepatient's rib, gradually developing a safe hold on the rib whileprotecting the neurovascular bundle throughout.

Ribs rotate about their attachments to the spine and sternum, presentinga challenge to avoiding contact with the neurovascular bundle.Addressing this, another important element of our design can include agap that avoids applying pressure to the neurovascular bundle regardlessof the relative rotations of the rib and SSF TRE (FIG. 134). Such a gapcan be formed by the space between a curved, descending SSF TRE shaftand a substantially flattened, or oblate spheroid fingertip mounted nearthe end of the shaft, making it impossible for the neurovascular bundleto impinge on the SSF TRE. The shape of such a space preserves a gap forthe neurovascular bundle regardless of the orientation of the patient'srib as it contacts the SSF TRE. Even more, this shape preserves aprotective gap for the neurovascular bundle over a wide range of ribsizes (i.e., patient sizes).

Still further, if a SSF TRE shaft is curved in a first plane, such afingertip might or might not be oriented substantially in that sameplane (FIG. 135). When retraction begins, a deviation of the oblatespheroid fingertip from the plane of the curve of the SSF TRE shaft canbe advantageous. For example the rounded, blunt limb of the oblatespheroid fingertip can be oriented to impinge very early (i.e., at verylow SSF TRE swing angles) upon the underside of the near margin of theadjacent rib, keeping the oblate spheroid fingertip low and the rib highright from the start, thus immediately presenting the protective gap tothe neurovascular bundle even at very low degrees of SSF TRE rotation.

So, the SSF TRE incorporates a first, flat profile shape for easyinsertion, a further, second SSF TRE profile shape providingmechanically automatic reorienting to the patient's tissues, and afinal, achieved SSF TRE profile shape that gently and safely appliesforce to the patient's tissues without impinging upon the neurovascularbundle under load.

Yet another feature of our device is that the SSF TRE can be designed sothat the tissue retraction elements are gathered up by, guided by, orcontained within a compliant, elastic, flexible sheath, for example anelastomeric cover (above). One advantage of including a rubber sheathwould be that the re-orientable tissue retraction elements are managedeasily in a flat, thin form during handling in an operating room, as thesurgeon inserts the tissue retraction elements. Another advantage isthat a compliant material can keep the surfaces of the SSF TRE smooth.Still another advantage of a compliant sheath is that, if resilient, theSSF TRE automatically re-flattens itself upon removing it from thepatient's incision, making the process of completing the surgery fasterand easier.

Helical Shape Rotates on Oblique Axis to Grab Tissues

The Tissue Retraction Element, all or in part, can be substantiallyhelical, creating a Helical Tissue Retraction Element (HTRE) (FIG.136A). The advantage of the HTRE shape is that a helix (or a portionthereof) can present to the incision a nearly straight, thin firstprofile shape in a first rotational position, and a curving, grasping,or engaging profile shape when in a second rotational position. Thehelically shaped TRE might be designed to rotate from the firstrotational position to the second rotational position under theinfluence of the forces experienced in the retraction process. This canbe facilitated by off-center loading as above, so that automaticreorienting is achieved as retraction begins.

The axis of rotation can be arbitrarily oblique, as desired. Further,helical shapes are naturally gradually curved, so that the transitionfrom a first profile orientation to a second profile orientation can beextremely smooth, gradual and without sudden changes in aspect orloading to the patient's tissues.

Still further, a smooth, helical TRE form can be designed so that all ora part of the process of inserting the tissue retraction elements intothe incision automatically reorients the HTRE (FIGS. 136B and 136C). Tofacilitate this, the radius of curvature of such a helix forming theHTRE need not be constant over its depth. For example, if the lower,more vertical portion of an HTRE (with a small radius and a high pitchangle) presents a thin profile shape to the incision, so easinginsertion (FIG. 136B), the overall helical form can be such that theupper portion of that HTRE (with a larger radius and lower pitch angle)smoothly impinges on the margin of the incision to drive HTRE rotationfrom a first rotational position to a second rotational position (FIG.136C).

Tissue Retraction Elements on an Improved Thoracic Retractor

FIG. 137 shows some improved Tissue Retraction Elements as mounted on aautomated thoracic retractor L50. The retractor L50 is motorized andautomated. Tissue engagers L60 are for thoracotomy. A hand-heldcontroller L70 communicates with retractor body L80 through cable L90.

FIG. 138 shows an embodiment of a complete retractor L00 for reducingthe trauma to ribs during retraction for thoracotomy. Retractor L100comprises a linear drive element L05 aligned with the direction ofretraction L10. Retractor L00 has a first arm L15 and a second arm L20oriented substantially perpendicular to the direction of retraction L10with at least one of the arms L15 and L20 being moveable along lineardrive element L05. For the purposes of this discussion two axes areimportant: first, the direction of retraction L10 and a vertical axisL11 that is approximately normal to a plane that is parallel with theskin of a patient. Each arm L15 and L20 have a self-balancing tissueengager associated with each arm. The two arms and associatedself-balancing tissue engagers presented here are symmetrical, with thetwo self-balancing tissue engagers being mirror images, but asymmetricalassemblies can be made. Due to the symmetry here, description of onlyone arm and balancing assembly will suffice.

Consider first arm L15 in FIG. 139. Self-balancing tissue engager L25comprises a first rotatable joint L105 that joins arm L15 to firstbalance bar L110 such that the middle L115 of first balance bar L110attaches to the end L120 of arm L15. First rotatable joint L105 thuspermits rotation about an axis L125 that is oriented approximatelyperpendicular to the direction of retraction L10 and approximatelyparallel to normal axis L11. First balance bar L110 has a first end L130and a second end L135. Two second rotary joints L140 are located onfirst balance bar L110, with a second rotary joint L140 being placed ateach of the two ends, first end L130 and second end L135, of balance barL110. Both second rotary joints L140 permit rotation about an axis L145that is oriented approximately perpendicular to the direction ofretraction L10 and approximately parallel to normal axis L11. A secondbalance bar L150 attaches at its middle L155 to each of the rotaryjoints L140 on first end L130 and on second end L135 of first balancebar L110. Two third rotary joints L160 are located on second balance barL150, with a third rotary joint L160 being placed at each of the twoends, first end L165 and second end L170, of second balance bar L150.Both third rotary joints L160 permit rotation about an axis L175 thatalso is oriented approximately perpendicular to the direction ofretraction L10 and approximately parallel to normal axis L11. Adescender post L180 attaches to third rotatory joints L160 as shown inFIG. 140 to permit rotation L185 of descender post L180 in the incisionof the patient.

Note that there are, thus, four descender posts L180 in eachself-balancing tissue engager L25. The combination of rotary jointsL105, L140, and L160 with the first and second balance arms L110 andL150, respectively, creates a doubletree as described in SectionF—Self-balancing Retractor Blades. Thus, the first balance bar L110 is adoubletree balance bar and the second balance bars L150 areswingletrees.

FIG. 140 shows a descender post L180 having a unique shape that enablessure engagement of a rib L205 without touching the neurovascular bundleL210. The cranial direction is the direction of retraction L10. Rib L205is the cranial-most rib at the incision. Descender post L180 pushesagainst caudal margin L215 of rib L205 to retract rib L205. Descenderpost L180 comprises an elongate member L220 having a first end L225 anda second end L230, a first rib-forcing surface L235 adjacent to secondend L230, a hook element L240 disposed adjacent the second end L230 ofthe elongate member L220, the hook element L240 comprising a first hookend L245 and a second hook end L250, and a second rib-forcing surfaceL255 between first hook end L245 second hook end L250, thereby defininga gap region L260 between the first rib-forcing surface L235 and thesecond rib-forcing surface L255. The gap region L260 is concave andpossesses a length L265 along the direction of retraction L10 configuredto place the second rib-forcing surface L255 substantially away from theneurovascular bundle L210.

The placement of second rib-forcing surface L255 should be such thatsecond rib-forcing surface L255 contacts the bottom of rib L205somewhere in the mid-region along the chord L270 of the rib L205, fromapproximately 20% to 80% from the caudal margin L215 of rib L205. Thisplacement is important to ensure that neurovascular bundle L210 ispositioned in the gap region L260 such that no part of descender postL180 contacts or in any ways exerts a force on neurovascular bundleL210. A descender post L180 on the opposite side of the incisionretracting a caudal rib (not shown) does not have this considerationbecause the neurovascular bundle L210 is not on the cranial margin L280of a rib. Nevertheless, descender posts L180 work well for the caudalrib, too.

FIG. 141 shows a descender post having a different shape, being morehook-shaped, like the descender post shown in FIG. 98A. FIG. 141 is aphotograph from a thoracotomy in a 50 kg pig. It is clear in thispicture there is a large gap region and that the neurovascular bundle isnot being touched.

The axis of rotation L175 of third rotary joint L160 is shown in FIG.140 and is positioned at the first end L225 of elongate member L220.Rotation about axis L175 causes first rib-forcing surface L235 to swingthrough an arc having substantial radius L275. FIG. 139 shows adescender post L180 in two positions, position L300 with the descenderpost aligned approximately perpendicular to the direction of retractionL10 and position L310 with the descender post L180 aligned approximatelyparallel to the direction of retraction L10. Position L310 is thedeployed position, the position the descender post L180 assumes duringretraction. Position L300 is the undeployed position. If all descenderposts are in position L300, then the hook element L240 alignsapproximately parallel with the incision, easing insertion between theribs. This is the situation depicted in FIG. 130A. As retractioncommences, the force at first rib forcing surface L235 causes descenderpost L180 to rotate into position L310. Thus descender posts L180 inself-balancing tissue engager L25 can self-deploy. The surgeon caninsert both self-balancing tissue engagers into the incision with hookelements L240 of all descender posts L180 aligned approximatelyperpendicular to the direction of retraction (and thus parallel with themargins of the two ribs adjacent the incision). When retractioncommences, the force applied to the first rib-forcing surfaces L235 onall descender posts L180 on both sides of the incision causes alldescender posts L180 to automatically rotate into the deployed positionL310 with second rib-forcing surface L255 coming into proper positionunder the rib, as depicted in FIG. 130B.

An elastic element can be added to self-balancing tissue engager L25both to hold all components (balance arms and descender posts) in theirundeployed position L300. This makes retractor L00 easier to handle.When the retractor is loaded, the elastic element only lightly opposesthe forces at first rib-forcing surfaces, allowing the descender postsL180 to rotate into position L310 and the balance arms to balance theforces on the descender posts L180. Furthermore, when retraction isreleased, the elastic element will exert a light force to return thedescender posts L180 to their undeployed position L300 facilitatingremoval from the incision. The elastic element can include simple rubberbands or other elastomeric components deployed at joints. Alternately,an elastomeric layer could be placed over the entire self-balancingtissue engager L25, such as would occur on coating the self-balancingtissue engager during a dip or molding process.

Elastomeric components can also be placed at the rib-forcing surfaces topad the rib at those surfaces. These pads can be soft, but the pad atthe first rib-forcing surface L235 should not be so thick as to deforminto the gap region L260 and apply pressure to the neurovascular bundleL210.

The embodiments set forth herein are examples and are not intended toencompass the entirety of the invention. Many modifications andembodiments of the inventions set forth herein will come to mind to oneskilled in the art to which these inventions pertain having the benefitof the teaching presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinventions are not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areused herein, they are used in a generic and descriptive sense only andnot for the purposes of limitation.

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1. A thoracic retractor for performing a thoracotomy, comprising: alinear drive element defining a direction of retraction; at least twoarms oriented substantially perpendicular to the direction ofretraction, at least one of the at least two arms moveable along thelinear drive element; and at least one self-balancing tissue engagerassociated with each arm, the at least one self-balancing tissue engagercomprising: a first rotary joint defining a substantially vertical firstaxis of rotation associated with the arm; a first balance bar having twoends, and attached between the first balance bar's two ends to the firstrotary joint; and the first balance bar's two ends each having a secondrotary joint having a substantially vertical second axis of rotation,two second balance bars, each having two ends and each two ends eachhaving a third rotary joint having a substantially vertical third axisof rotation, about each of which rotates a descender post descendingfrom the ends of the second balance bars. Thus four descender posts areon each self-balancing tissue engager.
 2. The device as in claim 1,where there are two, opposing self-balancing tissue engagers, eachcomprising: one doubletree balance bar unit, comprising: two swingletreebalance bars, one on each end of the doubletree balance bar; and onedescender post on each end of the swingletree balance bars, for a totalof four descender posts.
 3. A tissue engager for a thoracic retractorfor performing a thoracotomy, comprising: at least one balance baroriented substantially perpendicular to a direction of retraction andcapable of moving along the direction of retraction; at least onedescender post descending from the at least one balance bar, thedescender post comprising: an elongate member having first and secondends and a first rib-forcing surface adjacent the second end; a hookelement disposed adjacent the second end of the elongate member, thehook element comprising a first hook end and a second hook end, and asecond rib-forcing surface adjacent the second hook end, therebydefining thereby a gap region between the first rib-forcing surface andthe second rib-forcing surface; and the gap region being concave andpossessing a length along the direction of retraction configured toplace the second rib-forcing surface substantially away from theneurovascular bundle.
 4. The tissue engager of claim 3, where theconcave shape of the gap region is further defined as a tapered hollowdefining a taper point.
 5. The tissue engager of claim 4, where thetaper forms an acute angle.
 6. The tissue engager of claim 4, where thetaper is logarithmically curved.
 7. The tissue engager of claim 4,comprising a plurality of the descender posts.
 8. The tissue engager ofclaim 7, wherein the plurality of descender posts are comprised of aplurality of balanced descender posts.
 9. A tissue engager for athoracic retractor for performing a thoracotomy, comprising: at leastone retraction bar capable of moving along a direction of retraction; atleast one descender post descending from the at least one retractionbar, comprising: an elongate member having first and second ends and afirst rib-forcing surface adjacent the second end; and a hook elementdisposed adjacent the second end of the elongate member, the hookelement comprising a first hook end and a second hook end, and a secondrib-forcing surface adjacent the second hook end; and the at least oneretraction bar further comprising at least one rotational mountconfigured to rotate about a first rotational axis orientedsubstantially vertical with respect to a plane of a patient's skinengaged by the at least one descender post.
 10. The device as in claim9, wherein the at least one descender post is substantially curved, andwhere the first rib-forcing surface projects a nonzero distance radiallyout away from the substantially vertical axis, defining thereby a momentarm reaching out from the substantially vertical axis to the firstrib-forcing surface.
 11. The device as in claim 9, wherein the curveddescender post is configured to rotate about the substantially verticalaxis by at least 90 degrees.
 12. The device as in claim 1, where theself-balancing tissue engagers are associated with an elastic elementthat confers the property of elastic recoil upon the self-balancingtissue engagers.
 13. The device as in claim 1, where the first jointaxis is associated with an elastic element.
 14. The device as in claim1, where the second joint axis is associated with an elastic element.15. The device as in claim 1, where the third joint axis is associatedwith an elastic element.
 16. The device as in claim 1, where theentirety of the self-balancing tissue engagers are substantiallyencompassed by an elastic sheath.
 17. The device as in claim 10, wherethe Young's modulus of the elastic element is between 0.1 MPa and 60MPa, first, permitting the preservation of the curved descender posts asa flat array for easy handling and insertion, and second, permitting thegentle, automatic deployment of the curved descender posts as retractionbegins, and third, permitting the automatic re-flattening of the arraycurved descender posts as the surgeon closes the patient's incisionafter the procedure.
 18. The device as in claim 3, where the Young'smodulus of the elastic element is between 0.75 MPa and 1 MPa.
 19. Thedevice as in claim 10, where the elastic element is spatially associatedwith the gap region, and provides a padded surface to the patient'ssurrounding tissues.
 20. A method for retracting thoracic tissue,comprising: retracting thoracic tissue in the direction of a lineardrive element by moving along the linear drive element at least one oftwo arms oriented substantially perpendicular to the direction ofretraction; while engaging the tissue with each arm using aself-balancing tissue engager attached to each arm, while theself-balancing tissue engager automatically balances the forces amongstfour descending posts.